Can not mount NAS Server on Windows 7 Machine

I have two NAS Servers in a network. Also I have two Windows 7 machines and one Windows XP machine. One of those Windows 7 machines is not able to mount the NAS servers! I can ping both servers successfully but I cannot access them. I am getting an error saying this path is not accessible with the errorcode 0x80070035.

I assume it has something to do with my Windows 7 installation but I don't want to reinstall until I haven't tried everything. Do you have an idea what I can do here? Let me know what additional informations you need to help me :-) Thank's in advance

The issue was: A driver was missing. I was sure I had installed it before. It somehow got lost.

:-)