ISA Custom Forms

Hello,

We have a problem creating custom forms on ISA 2006. The default ones work fine but if I copy the 'ISA' folder for example (under CookieAuthTemplates), name it something else, then set the new name either on the listener or the publishing rule we get the following error when accessing the pages -

Error Code: 500 Internal Server Error. The data is invalid. (13)

Has anyone seen this before?

I've seen a few people talking about disabling HTTP compression but this doesn't seem to have made any difference.

Thanks in advance,
Chris