Computername/username Network Issue

I have installed Windows 7 ultimate and have a server with Win server 2003 installed on it.

On my main pc (with Windows 7) I have two user-accounts, both administrator rights. Both users have access-rights to the server. User one (myself) can access the server without any problems. However, user two (my girlfriend) cannot get access!

When making a network-connection, it asks for username/pw. If I fill this in, I immediately get a new username/pw screen, however this time it gives me COMPUTERNAME/User to fill in.

Obviously, my server does not recognize COMPUTERNAME/User, so my girlfriend cannot get acces to the server. The strange thing is that if she use the option to use a different user, and fill-in MY username/pw, it works ok (only till she reboots the pc and logs-in again...).

If have seen advise like "look for the entry "Network Security: LAN Manager authentication level" and open it. Click on the dropdown menu and select "Send LM & NTLM - use NTLMv2 session security if negotiated". I tried all of that, but nothing seems to work

I had no problems what so-ever when using XP on my main PC, so their is definately nothing wrong with the settings on the server (admin rights etc.).

For some reason, I once managed to get access to the server under my girlsfriends account, but the next time she logged-in, noaccess was made and never ever since then.

I already setup a third user on my server with all right, made that user active under Windows 7, but I faced the same isssues as my girlfiends account. only the account of myself seems to work?