newbie in CVS

situation:
I have a cvsd server running on Ubuntu, containing my VB code

Problem:
Most projects use the same very common classes (stored in directory "commonclass_directory").

I know I can use the ampersand(&) sign in the "modules" file for this, but how do I make sure that the "commonclass_directory" doesn't end up in top of the project directory? I need these common classes to appear in a sub directory, where VB needs them.

I tried out all combinations of -d, -a and what not options, and got very far.
Checking out two projects (both using this commonclass) appears to be fine, but committing a change in the second ends up with the message:

"cvs commit: Up-to-date check failed for `commonclass_directory/commonclass.vb'
cvs [commit aborted]: correct above errors first!"

(updating first says: cvs update: conflict: `commonclass_directory/commonclass.vb' is modified but no longer in the repository)

Please help me with my modules file (search everything and every help found states the -d and -a options as very obvious things to use).

General_Project1
 |
 +-- Some_sub_dir1
      |
      +--commonclass_directory
      |
      +-some_subsubdir1

General_Project2
 |
 +-- Some_sub_dir2
      |
      +--commonclass_directory
      |
      +-some_subsubdir2

Obviously I want to be able to change, update, commit inside the commonclass_directory at will.