[AccessD] Access ade 20 User limit?

We have an Access XP ade which will only allow 20 users to 
simultaneously have it open.  The 21st user gets a "Database is not 
in the correct file format" error (or words to that effect).

 From googling it seems that the only solution is to provide more 
copies of the FE so that the limit doesn't get reached.

Has anyone else come across this problem and found a better solution?

Regards

David Emerson
Dalyn Software Ltd
Wellington, New Zealand