"HTTP 500 - Internal Server Error"

This error may occur when web server or PHP is mis-configured in some way. This error is usually shown by Internet Explorer.

First thing that you need to do, to fix the issue that caused this error, is to see the real error message.

Go to Tools > Internet Options > Advanced Tab and uncheck "Show Friendly HTTP Error Messages".

Then refresh the page and you can see the real error in web server configuration that needs your attention.

If that won't help, enable error logging and examine error log file for additional information.