I've just got a Mac and I can connect to shares on my Ubuntu server, read files and create directories but I cannot write. I get this error:

"The operation cannot be completed because you do not have sufficient privileges for some of the items."

I can connect from the command line with smbclinet and write fine. I have tried several different users on both the Mac (cannot write) and Ubuntu clients (can write).

Is this something to do with the ._filename files that finder creates?