500 error from .aspx Urls in Wordpress

I'm having trouble redirecting old .aspx urls to a wordpress url.

For some reason, in this particular install, any url with .aspx on the end gives a 500 internal service error, when other installs just show page not found.

I presume it is something to do with a hosting setting not enabled, does anyone know what it might be?

ASP.net wasn't natively supported on my hosting, and had to be turned on manually.

If anyone wanted to know ^^