More than likely your message contains a special character like the Euro or British pound symbols.
The forum gags on those types of characters and it has resulted in problems with sending U2Us and posting to threads.
I just created a U2U and tried to used the Euro symbol (
) and got the exact error message you describe.
ATB,
Sam
"I never had any friends later on like the ones I had when I was 12 - Jesus, does anyone?" - The Body by Stephen King