I have synced my X: drive with my project code from the SVN repository. I am using jdk1.5.0_06 with apache-tomcat-5.5.20. Now on starting up I can see an error saying "Target runtime apache-tomcat-5.5.16 is not defined.AuthADWSUnknown119220314465438667"
In the Package Explorer, I can see the red error mark for the AuthADWS web service but when i expand the WS no modules are error marked.
I think you copied the entire Eclipse workspace along with the source code. Eclipse stores information about the runtime server that was created for a workspace.
As per your post, it seems to suggest that the server eclipse is trying to look for is of a lower version (Which may have been valid installation on someone else's system) and the one you have is a higher version.
Try creating a new runtime server and delete the old one pointing to lower version of web server.