Real bizzare problem with logging in... IIS/MSSQL... help?

[papirov]

First of all, thank you for the wonderful product to the authors...

I seem to have a super duper weird problem... I'm a brand new user to the Webmail product... and frankly very new to PHP as well..

I'm trying to install Roundcube on IIS7/MSSQL2008... I followed all of the tutorials that explain what needs to do be done to do so and seem to have configured the MSSQL, IIS and IMAP properly...  I know Roundcube is able to make a sucessfull connection to IMAP server and SQL server.

I've gotten the Login screen from Roundcube, am able to enter my credentials and press Login.  Upon the login I get the following error:

PHP Error in C:\inetpub\wwwroot\mail\program\include\rcube_user.php (399): Failed to create new user.

I've checked the SQL tables out, and the system is able to make the connection to SQL server and *gasp* is able to create rows in the 'users' table.  (I had to make one of the columns NULLable to get that far)...

The error seems to occur on line 368 of the rcube_user.php file:
if ($user_id = $dbh->insert_id(get_sequence_name('users')))

It appears that for some unknown reason the system is not able to get back the newly inserted identity value, although table is configured properly.

I've tried outputting the result of either $user_id or insert_id() function in the error message and have gotten back empty string.

Any clues at all?  I'm losing my mind here as to what could be the problem.  

Thank you kindly!