*UPDATE* This issue is now resolved.
We're aware of a problem with some Samsung devices whereby launching the My5 or Milkshake application results in the following error:
Service Error - Unknown Error Occurred
We apologise for the inconvenience. We have determined the cause of the issue and are working with our external providers to have this resolved as soon as possible.
In some circumstances, this can be resolved by upgrading the firmware on the TV as instructed here.