If you are receiving ERROR 500 when attempting to access the CRM webpage just follow these steps to fix the issue
1. Go to the machine where the CRM was originally installed
2. Go to the Start menu
3. search for " services"
4. Open the Services screen\
5. in the list of services locate ASP.NET STATE SERVICE
6. right click on ASP.NET STATE SERVICE and select START
7. right click again on ASP.NET STATE SERVICE and go to PROPERTIES
8. Make sure that the " startup type" is set to AUTOMATIC. If it is set to anything else, then change it.