Ubuntu – Unable to mount CIFS share from /etc/fstab

I have a line in my /etc/fstab for ages that stopped working since 13.04:

//192.168.100.2/share   /mnt/popcorn      cifs username=MyUserName,password=MyPassword,user,gid=sambashare,file_mode=0664 0   0

and it gives me:

mount /mnt/popcorn
mount error(13): Permission denied
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

dmesg is as helpful as sunshine in the desert:

[  622.471321] CIFS VFS: Send error in SessSetup = -13
[  622.471458] CIFS VFS: cifs_mount failed w/return code = -13

I know the user/pass combo is correct, as this works fine:

bart@dosar:~$ smbclient //192.168.100.2/share --user=MyUserName
Enter nmt's password: 
Domain=[WORKGROUP] OS=[Unix] Server=[Samba 3.0.32]
smb: \> ls
...

How can I permanently mount a CIFS/Samba share on Ubuntu 13.04 ?