Hey Geoffrey,
First, does the message say server preferences or network preferences? I know we've seen the latter message before, that's what I was thinking of when I said we've seen this. With that message it turned out to be the product activation. Second, can you confirm for us which version of Dreamweaver you're using. Please let us know the full version number which you should be able to find in the About dialog box.
Regardless, if it does say "network" instead of "server", it might still be that issue even though your product is activated. Here is the thread with the discussion and our advice:
http://forums.adobe.com/message/3914305#3914305
As you can see in that thread there is a link to a KnowledgeBase article ( http://kb2.adobe.com/cps/846/cpsid_84665.html ) that discusses how to disable CSLive. Disabling CSLive is another way to get this issue. That discussion is for Windows, but the KnowledgeBase link contains directions for Mac. Look at (but don't actually perform) those steps for Mac to check your registry to see if you have that key and what the value is. If it is set to zero it is probably the cause of your problem. If not, then follow up with me here and I'll have you send me a log file from your system so we can look into this further.
Thanks,
Mark
