Jason, I fixed it.
Under the Dreamweaver preferences in the site category FTP time out was set to two seconds. No way, FTP can connect in 2 seconds, so I set it to 80 seconds and voila ... it worked. What really puzzles me though is the fact, that I had never problems with the the FTP connection. I wonder if some bug could have changed the setting, becausee I most certainly did not.