What is your request path when you get this error?
I'm guessing there's some sort of config problem giving bad characters in the path.
Thanks, this problem has changed into a different one while we were upgrading from 7.5 to 7.7.1 but I'll close this and create a new question for that (404 errors when attempting to view plugin now)
I have an ASPX page within a plugin that was working fine when it was a public Add-on, but since I moved it to be a protected add-on and the files go into the/appdata/ directory rather than the wwwroot folder it now gets a "A potentially dangerous Request.Path value was detected from the client (<)." error when the page first loads >).">
I obviously don't want to make any changes to the overall site web.config as this module needs to work out of the box - have I missed some setting within the add-on or the aspx page in order to run it properly as a protected module?
Many thanks