MSSQL Database connection problem - hard to solve?

[eluser]Unknown[/eluser]
Hello! I've just started using CodeIgniter, my first framework, before that I used to successfully write my scripts from scratch.

Ok the problem is that my CI has problems with connecting to MSSQL (2008) while my non-CI script doesnt have!

By problems I mean that it does connect to database but sometimes it doesn't.
It prints 'Could not select database...', when I refresh it, it works again.

So, sometimes it happens like this:
Person fills the form, clicks submit and then the message 'Could not select database' is shown, the person has to hit f5 to resend the content and then it works.

Thank you.