Add Spring Project Nature not shown in some projects

[Zmaj]

Hello,

i have the problem that the option of adding spring project nature to a existing project is not shown with some of my projects.
The thing is that it works withe some projects and there is no real difference
between the working and the not working ones.
All are JEE projects using spring and hibernate. When the projects are closed
the option "Add spring project nature" is shown with all projects,but as soon as i open up its gone.
First i thought it may have to do something with eclipse user libraries because
in the two projects it does not show up all spring and hibernate dependencies
were resolved with user libraries. The projects that work have all the jars
directlly in the app lib folder.
But after adding the jars directlly to lib and removing the user library it still remaind the same . Any ideas ?
I use sprigide2 RC2 with eclipse 3.2.2 callisto and wtp 1.5.4...
Zmaj