This is just a case of a bad error message in CVS; probably someone will get around to fixing it sooner or later, but meanwhile it may bite you. The error message looks something like this:
floss$ cvs co -d bwf-misc user-space/bwf/writings/misc cvs server: cannot find module `user-space/bwf/writings/misc' - ignored cvs [checkout aborted]: cannot expand modules
CVS appears to be saying that there's something wrong with the CVSROOT/modules file. However, what's really going on is a permission problem in the repository. The directory I'm trying to check out isn't readable, or one of its parents isn't readable. In this case, it was a parent:
floss$ ls -ld /usr/local/cvs/user-space/bwf drwx------ 19 bwf users 1024 Aug 17 01:24 bwf/
Don't let that egregiously wrong error message fool you – this is a repository permission problem.