Site is running good, but giving internal server error while running scripts in jmeter

Website is running good, but at time of recording scripts it shows service unavailable and records nothing. website is password protected means need credentials to access website, So i always used to record the scenario after entering credentials. And whenever I used to run that recorded script it shows and failure message in response : Service Unavailabe and Response Code: 500

I already added Authorization Manager in the scripts as it gets recorded in it.

but nothing works.Earlier we were able to run scripts very fine but we have some changes in website.but not able to debug the cause of this. Please help me to find the reason

Thanks Chiranjeevi