'Ambiguous mapping found' in controller with one POST mapping, why?

[blandger]

Hi guys.
I'm using Spring 3.2.0.RELEASE, Security 3.1.3, MVC + WebFlow 2.3.1, Spring Social + Spring Social Security (both snapshoot), + Spring mongodb stuff.

Spring Social + Spring Social Security initially have Spring 3.1.3 dependency, but I recompiled them with Spring 3.2.0.RELEASE locally and installed by gradle build script.

I'm trying to create 'FB canvas' app and have one controller with ONE ONLY post method and I'm getting error above.

@Controller
public class CanvasProviderSignInController {
...... // internal variables initialized by constructor....

    @RequestMapping(value = "/canvas", method = RequestMethod.POST)
    public String processFaceBookCanvasRequest(
            NativeWebRequest request) {
..........
return NULL!!!;
}


Controller initialization:

@Configuration
public class SocialAndSecurityConfig {
    @Inject
    private Environment environment;
....... // different stuff


   	@Bean
   	public CanvasProviderSignInController providerSignInController() {
           CanvasProviderSignInController signInController = new CanvasProviderSignInController(
                   socialAuthenticationServiceLocator(),
                   facebookServiceProvider(),
                   usersConnectionRepository(),
                   signInAdapter(),
                   signedRequestDecoder()
           );
          return signInController;
   	}
..........

I even removed all code from method returning NULL only, but I'm getting error:

20:51:39.015 [RMI TCP Connection(3)-127.0.0.1] ERROR o.s.web.context.ContextLoader - 
Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'requestMappingHandlerMapping' 
defined in class path resource [org/springframework/web/servlet/config/annotation/DelegatingWebMvcConfiguration.class]: 
Invocation of init method failed; nested exception is java.lang.IllegalStateException: Ambiguous mapping found. 
Cannot map 'providerSignInController' bean method 
public java.lang.String 
com.web.controller.facebook.CanvasProviderSignInController.processFaceBookCanvasRequest(
org.springframework.web.context.request.NativeWebRequest)
to {[/canvas],methods=[POST],params=[],headers=[],consumes=[],produces=[],custom=[]}:
 There is already 'canvasProviderSignInController' bean method
public java.lang.String 
com.web.controller.facebook.CanvasProviderSignInController.processFaceBookCanvasRequest(
org.springframework.web.context.request.NativeWebRequest) mapped.
.............
Caused by: java.lang.IllegalStateException: Ambiguous mapping found. Cannot map 'providerSignInController' bean method 
public java.lang.String 
com.web.controller.facebook.CanvasProviderSignInController.processFaceBookCanvasRequest(
org.springframework.web.context.request.NativeWebRequest)
to {[/canvas],methods=[POST],params=[],headers=[],consumes=[],produces=[],custom=[]}:
There is already 'canvasProviderSignInController' bean method
public java.lang.String 
com.web.controller.facebook.CanvasProviderSignInController.processFaceBookCanvasRequest(
org.springframework.web.context.request.NativeWebRequest) mapped

Is there chance something is wrong with libraries? Here is the list.

activation-1.1.1.jar
aopalliance-1.0.jar
attoparser-1.1.jar
commons-beanutils-1.8.0.jar
commons-codec-1.6.jar
commons-collections-3.2.1.jar
commons-digester-2.0.jar
commons-lang-2.4.jar
commons-logging-1.1.1.jar
guava-13.0.1.jar
hibernate-validator-4.3.1.Final.jar
httpclient-4.2.2.jar
httpcore-4.2.2.jar
jackson-core-asl-1.9.9.jar
jackson-mapper-asl-1.9.9.jar
javax.inject-1.jar
jboss-logging-3.1.0.CR2.jar
jcl-over-slf4j-1.7.1.jar
joda-time-2.1.jar
jstl-1.2.jar
logback-classic-1.0.9.jar
logback-core-1.0.9.jar
lombok-0.11.6.jar
mail-1.4.5.jar
mongo-java-driver-2.10.1.jar
sitemesh-3.0-alpha-2.jar
slf4j-api-1.7.2.jar
spring-aop-3.2.0.RELEASE.jar
spring-beans-3.2.0.RELEASE.jar
spring-binding-2.3.1.RELEASE.jar
spring-context-3.2.0.RELEASE.jar
spring-context-support-3.2.0.RELEASE.jar
spring-core-3.2.0.RELEASE.jar
spring-data-commons-core-1.4.0.RELEASE.jar
spring-data-mongodb-1.1.0.RELEASE.jar
spring-expression-3.2.0.RELEASE.jar
spring-jdbc-3.2.0.RELEASE.jar
spring-js-2.3.1.RELEASE.jar
spring-js-resources-2.3.1.RELEASE.jar
spring-security-acl-3.1.3.RELEASE.jar
spring-security-config-3.1.3.RELEASE.jar
spring-security-core-3.1.3.RELEASE.jar
spring-security-taglibs-3.1.3.RELEASE.jar
spring-security-web-3.1.3.RELEASE.jar
spring-social-config-1.1.0.BUILD-SNAPSHOT.jar
spring-social-core-1.1.0.BUILD-SNAPSHOT.jar
spring-social-facebook-1.1.0.BUILD-SNAPSHOT.jar
spring-social-facebook-web-1.1.0.BUILD-SNAPSHOT.jar
spring-social-security-1.1.0.BUILD-SNAPSHOT.jar
spring-social-web-1.1.0.BUILD-SNAPSHOT.jar
spring-tx-3.2.0.RELEASE.jar
spring-web-3.2.0.RELEASE.jar
spring-webflow-2.3.1.RELEASE.jar
spring-webmvc-3.2.0.RELEASE.jar
thymeleaf-2.0.16-SNAPSHOT.jar
thymeleaf-extras-conditionalcomments-2.0.0.jar
thymeleaf-extras-springsecurity3-2.0.0.jar
thymeleaf-extras-tiles2-2.0.0.jar
thymeleaf-spring3-2.0.15.jar
tiles-api-2.2.2.jar
tiles-core-2.2.2.jar
tiles-jsp-2.2.2.jar
tiles-servlet-2.2.2.jar
tiles-template-2.2.2.jar
validation-api-1.0.0.GA.jar
velocity-1.7.jar