HTTP Error 500 - Internal Server Error

Cause
The 500 Internal Server Error is a very common HTTP status code that means something has gone wrong on the web site's server but the server could not be more accurate on what the exact problem is.

Resolution
The 500 Internal Server Error is a "server-side" error, meaning the problem is not with your PC or Internet connection but instead is a problem with the web site's server.

Even though the issue is not yours to troubleshoot or resolve, there are a few things you can do:
1. Retry the web page by clicking the refresh/reload button or trying the URL from the address bar again. Even though the 500 Internal Server Error is reporting a general error on the web site's servers and not your computer, the server error may only be temporary.



Trying the page again will often be successful.

Note: If the 500 Internal Server Error message appears during the checkout process at an online merchant, be aware that duplicate attempts to checkout may end up creating multiple orders - and multiple charges! Most merchants have automatic protections from these kinds of actions but it's still something to keep in mind.

2. Come back later. The 500 Internal Server Error message is one of the most common error message seen when checking out during an online purchase so sales are often disrupted. This is usually a great incentive to resolve the issue very quickly.

3. If you can't wait any longer for the problem to be resolved or if you'd like to help out, you may want to attempt to contact the webmaster or another website contact and advise them of their server error.

The webmaster of most Internet sites can be reached via email at webmaster@website.com, replacing website.com with the actual website name.

Source:
http://pcsupport.about.com/od/findbyerrormessage/a/500servererror.htm