Farouk,
It sounds like this may be your first time using CVS. CVS (Concurrent Versioning System) has a concept of checking out a module, which you have already implicitly done by sharing it. From now on, you GET changes from the CVS server by doing and UPDATE and you SAVE changes into the CVS server by doing a COMMIT. That is it. There is no “checking out” then “checking back in” like in VSS. There aren’t even native edit locks in CVS, although I believe they are support with later copies of CVS.
The ‘C’ in CVS is the key here, ‘Concurrent’, everyone can work on everything at the same time and CVS will merge the changes. When there is a merge conflict, Eclipse will present you with the two files side by side and you have to merge the changes manually.
Farouk, please note that your question is outside the scope of this forum as this forum is for the MyEclipse product which focuses on J2EE development. If you need more help troubleshooting this, please address the Eclipse mailing lists as they will be able to provide more detailed information for you.