The password for our windows server 2003 account is very long and complex, so I don't want to enter it each time by hand when I log in via RDP. However, copy/paste in the login screen seems to be disabled, so I have to. Can this be triggered by some policy? Or is there another way to enable this?
You can create a RDP shortcut and keep the password saved in this- I would not advise that this is a good idea because of the security implications.
You can not do this. Sorry if this wasn't the answer you wanted. You don't want your password in your pastebuffer anyways. Huge security risk.
I use 1Password to solve this problem. It has an Auto-Type feature that avoids using the copy/paste buffer and types it into the password field. It's been many years since I switched over from KeePass but I'm pretty sure I used it to solve the same RDP problem. It has the advantage of being free but I much prefer 1Password.
I solved the problem by writing a small Autohotkey-Script that types the clipboard buffer after some seconds.