Here is a list of problems which do not fit into the above categories. They are in no particular order.
HOMEPATHin Environment variables). CVS expects the home directory to not end in a slash, for example C: or C:\cvs.
cvs updatefinds a conflict and tries to merge, as described in Conflicts example, but doesn’t tell you there were conflicts, then you may have an old version of RCS. The easiest solution probably is to upgrade to a current version of CVS, which does not rely on external RCS programs.