Windows Vista / samba - Can't open many instances of an applicatio

Hello. perhaps you can help me with this...

My company uses an ERP developed in something called OMNIS7. Its an old
application for Windows that runs even on Win16.

The ERP opens a database in a shared directory (its not a true client/server
app). This shared directory is on a RedHat 8 / Samba server. This server is
also the Domain controller for the Windows network.
We have a license for 30 users, so up to 30 users can open the ERP (and the
same database) at the same time. At least this was true for Win95 to XP, but
with Vista we have a problem:

In Windows vista we can't open 30 sessions at the same time. Let me explain:
Some of vista PCs join the network as Workgroup clients ('cos they are Home
edition) and other join as Domain clients (these are Bussiness edition).

Those PCs with Vista Home (workgroup client) can only open a single instance
of the program. If a second vista home tries to open a secont instance then
it gets a message from the program saying that there are too many
workstations in use (this is the license protection message of the ERP). In a
windows vista bussiness (domain client) you can open up to 3 instances but no
more.

The XP computers are not affected by this behavior: You can open 30
instances with no problem. Even if a few windows vista are already opened and
can't open more instances, the XP computers still can open more.

Its like Windows vista can detect the true amount of users opening the
database file. Or perhaps windows vista makes many connections to the
database and that waste licenses. I really don't know. And as you can imagin,
I can't access the source code of the ERP to debug this error.

Do you have any idea? Everything was fine before Vista, so maybe there is a
service configuration or a registry setting that makes Vista work as old XP
when it comes to shared directories.

Thank you.