CREATE DATABASE permission denied in database "master". An attempt to attach an auto-named database for file XXX failed.

i was having issue on asp.net 4.0 website on windows 2008 R2 server ,CREATE DATABASE permission denied in database ‘master’. An attempt to attach an auto-named database for file XXX failed.

i did some search on internet and then came to know that we need to give site access to netwrok user  as application was running under network service user (in default application pool) , i did tried to do so but error was not removed , then i just changed the user from network to local system in application pool and it started work without any issue.