Wrong Login details throws 500 Internal Server Error

[hs_jha]

I am trying to use roundcube mail for a small business firm.The server used is IIS7.
The problem is when you input wrong credentials for user name/email or password the page collapses with 500 internal server error

eg -

Username= sdsd
Password=sd


500 - Internal server error.
There is a problem with the resource you are looking for, and it cannot be displayed.I don't know how to find the actual error as i am new to this application. Kindly help...

[SKaero]

Whats in your error log?