500 Server Error is often a generic error that could really be something easy to fix in your code.
Have you configured the Enable Robust Exception handling in the Debug Output Settings section of the ColdFusion Administrator?
Allow visitors to see the following information in the exceptions page:
IIRC If you do not have this enableds ALL errors generated by your code is a 500 Server Error.
If you haven't or you don't want to enable robust expception (which one should not do on a production system. You want the hackers to get as liitte information as possible) The errors are probably stored in the ColdFusion logs, unless you have disabled this for some reason.
To add to Skinner's advice.
1. Check the log files that ColdFusion generates for the source of your errors.
2. Check the Windows event log to see if anything is logged there.
I should append to my original post the fact that Server 500 error also occurs when attempting to open the ColdFusion Server administration page
after extended periods of Server inactivity.
I, too, am having the exact same problem descirbed here.
ColdFusion 9 64-bit
Windows 2008 Server 64-bit
After successfully installing Coldfusion9, I let the admin console sit idle for about an hour or so and when returned got 500 errors. Restarting IIS and/or Coldfusion does not resolve it. I cannot access the CF admin console because of the 500 error. No indication of cause in any log. Cannot set verbose setting as described in this forum because I don't have an admin console. Need help.
Go through this link it might help you ,....
Thank you for sending this along...Unfortunately, it did not fix the problem.