receiving internal server error on connecting salesforce through OAuth2

Question

I've started testing the oauth2 auth, However, when I use the correct credentials(of Sandbox Environment), (grant_type: password) I get an Internal Server Error (500 response):

An internal server error has occurred

An error has occurred while processing your request. The salesforce.com support team has been notified of the problem. If you believe you have additional information that may be of help in reproducing or correcting the error, please contact Salesforce Support. Please indicate the URL of the page you were requesting, any error id shown on this page as well as any other related information. We apologize for the inconvenience.

It works fine with developer edition credentials.

I have checked out the below links, but could not able to found any solution.

http://salesforce.stackexchange.com/questions/20559/what-is-the-use-of-setting-oauth-callback-url-as-https-login-salesforce-com-se

http://gersic.com/oauth-2-0-for-salesforce-com/

https://developer.salesforce.com/forums/?id=906F00000009CYeIAM

Please help me in this.

Thanks in advance.