HTTP Error 503. The service is unavailable.

HTTP Error 503. The service is unavailable.

Reason behind the error :-

This error comes when the default application pool is stopped or else  when the applicationhost.config and administration file are corrupted.

Solution :- This error can be resolved by starting the DefaultAppPool  from the IIS  but  some times even after starting the DefaultAppPool   from the IIS  the error will not get resolved .It is happened  when  both of the applicationhost.config and administration file are corrupted but luckily when we restarted  the iis , the iis will take the backup of  both applicationhost.config and administration  files and stored   on C:\inetpub\history folder   and  from this folder we can take the  copies of both files and replace in  to config folder (C:\Windows\System32\inetsrv\config)