Sheet Set Manager Switching Drawing to "Read Only"???? Autocad 2012 HELP!!

The problem we are having is drawings "automatically" switching to Read-Only when other users open the same drawing using the Sheet Set Manager. We've been using the Sheet Set Manager, in the same way, with the same amount of users, for years. The problem has only occurred recently.

Here's the problem:

User 1 will open drawing "A" thru the Sheet Set Manager. User 1 is now in drawing "A" with no problems.

Let's say about an hour later, while User 1 still has drawing "A" open, User 2 will open drawing "A" thru the Sheet Manager (User 2 should expect to see a window message saying that drawing "A" is in use and would you like to open it as a "Read-Only").

What then happens is the "glitch"....

User 2 does not get any message, and will end up opening drawing "A" as if no other user has it open (even though User 1 does in fact have it open).

User 1 (who has had drawing "A" open the entire time) will automatically switch to Read-Only???? And therefore will not be able to save the drawing. Even after User 1 closes drawing "A".

Anyone know what the problem is?

Any help is greatly appreciated!

Thanks,

Jeremy