RESOLUTION
This error indicates an error within .asp script. To determine the exact reason the following needs to be done:1. Disable custom error document for 500 error. This can be done directly using Plesk Control Panel: Plesk CP, Domains, domain.tld, Web directories, Error Documents tab, Find Error 500, Click on it, Select type `Default`.
2. Disable `Show friendly HTTP error messages` in the browser.
For example in Internet Explorer: Tool, Internet Option, Advanced tab, uncheck "Show friendly HTTP error messages", Click OK.
Then the exact error message and the error number are displayed. To find out the reason of the error, try searching the Microsoft support pages at using the error code: http://search.microsoft.com
Keywords: 500 Internal Server Error ASP