Cannot add web project to an EAR project

I have having a problem adding certain web projects to EAR projects.
Here is what I am doing:

In the EAR project, I open the "application.xml" file and then click
the "module" tab. In the modules area ( the top half of the screen) I
click the "Add" button.    A "Add Module" dialog window appears.  This
inlcudes a list of "projects found".

The problem is that the "projects found" list does NOT include the web
project that I need to add.  The web project in question was created
using the "new dynamic web" project wizard. Immediatly after running
the wizard, this project will appear in the list. But after I
syncronize the project with CVS, then it stops appearing in the list.

Any suggestions? Is there a file somewhere that controls whether or
not a web project can appear in the "projects found" list?

Thanks,
Sarah