Questions on action method


i am setting up rt for my company, so another one is using it ;).
anyway, i tried the email interface on manipulating tickets. it
works well, and i think the action queue is for this purpose
(manipulating tickets via email). if i am wrong then my following
questions might also be wrong.
i mail the action queue, the commands are executed as i expected,
but i alway get an error from rt:

There has been an error:
There has been an error with your request:

Your message is reproduced below:

and below the sent email with the headers and of course, without
any text in the body.
can some1 tell me how this works in more detail or what i might
have configured wrong that i get the error msg?\

thanks in advance