I to connected to a MsSQL server and I believe I found two errors:
1> The term "limit" is not valid SQL in Microsoft. Deleting "Limit 1" from all of the quires seemed to resolve the issue.
2> When connecting to MsSQL URL the port is separated from the host using a colon ":" it was coded to use a comma "," on line 257.
After making those changes it works great with MsSQL
http://wordpress.org/extend/plugins/external-database-authentication/