It probably would be best to open a support ticket with UBB.
You have logging turned on so if you see that generic database error it should be creating error logs. You can test it by opening control panel>Database tools -SQL COMMAND and submit a bogus query. It will create a error log entry. So I don't understand why you don't have any logs.
As far as mathx stated there are requirements for the connection pool. Can't find it now but I think 50 is the minimum suggested here.
