Comment 28 for bug 1113395

I had similar problems accessing a server in a domain and using a credential file. I solved the problem by specifying the domainname separatly (and not like before as part of the username.)

In the older Ubuntu (10.4) I had something like:
sudo mount -t cifs //MyServer/MyShare /mnt -o user=MyDomain\MyName,password=AskTheNSA

Now in 13.10 it did no longer work and I had to change it to:
sudo mount -t cifs //MyServer/MyShare /mnt -o domain=MyDomain,user=MyName,password=AskTheNSA

So if you are still not lucky to mount your share you might give this a try. If your server is not part of a domain, you might be lucky specifying your workgroup ...