It might be related to the post here:
Unable to post at Simple Modeling School-thread. Seems that the Apache's mod_security module is blocking some specific words that you are trying to send to the server in the POST command. Like when you try to enter
p y t h o n e r r o r in your message or signature, you get the same error. Even searching for
p y t h o n e r r o r fails. People on the SMF forums report more banned words, like
psychologist for example (seems to be working here).
