Hummmm,
There is access control in place - but its for the forms - and only blocks spammers trying to send us naughty weblinks.
For some reason, you seem to be getting a denied in the same way - but in theory this would be continuous if your address was blocked.
(So basically I have no idea)
If you get another 403 error, can you quickly goto
www.whatismyip.com and make a note of your IP address please.
This is the unique address linked to your web connection which may help me track why you are getting the occasional block.
KGAdmin