Its already been reported Sunshine at the SPNG forums
, It's a known bug and it has to do with what raceprouk said above. To fix it temporarily disable the Oversized Display Picture feature of SPNG (you can do this while the resize dialog is on your screen) by going into
Plus --> Preferences --> Plugins --> Stuffplug --> and unchecking "enable oversized display pictures"
After this you should without restarting msn be able to click ok and it should exit the dialog, if not restart msn and log in again. After you are in to your new account go back into the stuffplug preferences and re-enable this feature while still logged into your new account.