CI form not posting. on server, but working on localhost. gives error 500

[eluser]rudydelhi[/eluser]
Hi,

I am configuring a new site on server 1and1.com. Made a simple login form with username/password and trying to post the values, but it gives a strange error error

Error 500 - Internal server error
The server encountered an unexpected condition which prevented it from fulfilling the request.

This same script works well on my localhost. Tried every possible change in the config file and the form path.

Can any someone please out with this problem.

Thanks,
Rudy