Err99 is a somwhat common error encountered by Canon DSLR users. Because it is something of a catch-all error code a variety of causes and resolutions can be found via google. In my case the error was fixed by a firmware upgrade while it was in the hands of Canon camera servicing personnel, so if you find you have exhausted all options, send it back to Canon!
For what it is worth, the Camera already had what I thought was the latest firmware, perhaps I downloaded the wrong version, or Canon worked some additional magic.
Cheers,
Steve