This error can be caused by hidden characters in the email message subject line which can sometimes happen when copying from Microsoft Word and pasting into NetCommunity. Please follow the below steps to try and resolve the issue. 
  1. Open Message in NetCommunity
  2. Highlight and cut all the test from the subject line
  3. Paste text into notepad
  4. Remove all odd characters that do not belong
  5. Copy corrected text and paste into message in NetCommunity
  6. Try sending message again.
If the above steps do not resolve the error, please call into support for further assistance.