Do you have a StackTrace or any other details regarding this error?
A 500 error is fairly generic server-side error that could indicate a variety of things (compilation issues, exceptions etc). You might consider disabling custom errors within your web.config temporarily so that you can troubleshoot this issue. Additionally, you might try using the Developer Tools (F12) within your browser and monitoring the Network traffic (this will allow you to see the Request / Response of your specific calls and look into them a bit deeper to check for errors).
Fiddler is also an excellent tool for troubleshooting issues like these.