Tried that, but it doesn't work. I keep getting the error. The stupid part is that, after trying and entering the data once (and receiving the error), I can't try again. Then I receive the error immediately, not giving me the chance to simply try a different option. I need to log out and back again again before I can try again.

I also tried to install Samba via Synaptic (I guess it wasn't installed after all?), and since that the correct workgroup is shown, but it doesn't make any difference in connecting to the windows share.