I'm a bit perplexed about this exception. The class that cannot be found is on the classpath, and is referenced many times during execution prior to this exception being thrown. Does anyone have any ideas?

Code:
org.springframework.web.flow.execution.FlowExecutionStorageException: ClassNotFoundException loading the flow execution continuation -- this should not happen!; nested exception is java.lang.ClassNotFoundException: com.mycompany.domain.type.CustomType
java.lang.ClassNotFoundException: com.mycompany.domain.type.CustomType
        at java.net.URLClassLoader$1.run(URLClassLoader.java:199)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:187)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:289)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:274)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:235)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:302)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:219)
        at java.io.ObjectInputStream.resolveClass(ObjectInputStream.java:558)
        at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1513)
        at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1435)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1626)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1274)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:324)
        at java.util.HashMap.readObject(HashMap.java:1006)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:324)
        at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:838)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1746)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1646)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1274)
        at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1845)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1769)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1646)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1274)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:324)
        at org.springframework.web.flow.execution.impl.FlowSessionImpl.readObject(FlowSessionImpl.java:161)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:324)
        at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:838)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1746)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1646)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1274)
        at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1603)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1271)
        at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1845)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1769)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1646)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1274)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:324)
        at org.springframework.web.flow.execution.impl.FlowExecutionImpl.readObject(FlowExecutionImpl.java:445)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:324)
        at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:838)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1746)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1646)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1274)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:324)
        at org.springframework.web.flow.execution.FlowExecutionContinuation.getFlowExecution(FlowExecutionContinuation.java:99)
        at org.springframework.web.flow.execution.servlet.HttpSessionContinuationFlowExecutionStorage.load(HttpSessionContinuationFlowExecutionStorage.java:66)
        at org.springframework.web.flow.execution.FlowExecutionManager.onEvent(FlowExecutionManager.java:272)
        at org.springframework.web.flow.execution.FlowExecutionManager.onEvent(FlowExecutionManager.java:245)
        at org.springframework.web.flow.execution.servlet.ServletFlowExecutionManager.handle(ServletFlowExecutionManager.java:77)
        at org.springframework.web.flow.mvc.FlowController.handleRequestInternal(FlowController.java:137)
        at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:128)
        at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:44)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:684)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:625)
        at org.springframework.web.servlet.FrameworkServlet.serviceWrapper(FrameworkServlet.java:386)
        at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:355)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:760)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
        at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:358)
        at org.mortbay.jetty.servlet.WebApplicationHandler$Chain.doFilter(WebApplicationHandler.java:342)
        at net.sf.acegisecurity.util.FilterChainProxy.doFilter(FilterChainProxy.java:167)
        at net.sf.acegisecurity.util.FilterToBeanProxy.doFilter(FilterToBeanProxy.java:125)
        at org.mortbay.jetty.servlet.WebApplicationHandler$Chain.doFilter(WebApplicationHandler.java:334)
        at org.mortbay.jetty.servlet.WebApplicationHandler.dispatch(WebApplicationHandler.java:286)
        at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:567)
        at org.mortbay.http.HttpContext.handle(HttpContext.java:1807)
        at org.mortbay.jetty.servlet.WebApplicationContext.handle(WebApplicationContext.java:525)
        at org.mortbay.http.HttpContext.handle(HttpContext.java:1757)
        at org.mortbay.jetty.plus.PlusWebAppContext.handle(PlusWebAppContext.java:218)
        at org.mortbay.http.HttpServer.service(HttpServer.java:879)
        at org.mortbay.http.HttpConnection.service(HttpConnection.java:790)
        at org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:961)
        at org.mortbay.http.HttpConnection.handle(HttpConnection.java:807)
        at org.mortbay.http.SocketListener.handleConnection(SocketListener.java:218)
        at org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:300)
        at org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:511)