I think Filevista is not interfering with the admin folder (just a guess).
If you're running BE 1.6 or higher, in the Global.asax file, there's probably a "Application_Error" block of code. If so, (temporarily) remove that entire block of code (approximately 48 lines of code). This could be causing you to
see 500-Internal Server Error, rather than seeing an actual error message.
And/or in the web.config file, change the customErrors tag so it is:
If you're using IE, you may also be seeing IE's "friendly" error messages. You could try a non-IE browser, or in IE, you can turn this off under Tools -> Options -> Internet Options -> Advanced tab -> uncheck "Show friendly
HTTP error messages".
The purpose of these changes is to try and get an actual error message.