Due to undefined or strange requests to resources of server, your current request was declined with code 'Forbidden 403'.
Probably, you tried to use special symbols or combination of such symbols for sending on server together with usual text.
You need try more simple format of message. Or, may be, your web client contains suspicious files cookie.
In this case, cleaning files of cookies and cache memory of web client, can solve this problem.
Possibly existence of false-positive exception.
For solving with our help, you also can send specified ID (and URL) to special email address ID support for identification and solving of problem: