Please check two things for me and let me know.
1) Compare your .settings/org.jboss.tools.jst.web.xml against your co-workers. Does your co-worker have this file? If he/she does, it might point to libraries or JBoss runtimes that are located in different directories than what you checked into SVN with the project.
2) Verify that your co-worker's copy of JBoss Tools has the right project-level properties. I.e., check the Seam settings and verify that his/her Seam run-time path is right.
extreme - did that solve your problem ?
Sorry for my absence.
Thank you very much....but the problem is still there. I checked the files, all files are in the project, but it still doesn't work.
and your eclipse actually has jboss tools installed ? :)