Hi ,
I am tryign to login to Search head server.
It gives me error
500 Internal Server Error
The server encountered an unexpected condition which prevented it from fulfilling the request. Click here to return to Splunk homepage.
If i put wrong password it gives wrong password error. so looks like this is not related to authentication.
Check your default app/dashboard. I think you can get that error if the permissions changed on the app or dashboard and you no longer have access.