Login Internal Server Error

I've installed Gallery 2 previously a few times without a hitch. This time I went through the installation without any problems and everything looked ok. Then when I tried to login I got Error 500 - Internal Server Error. I found that if I entered incorrect login info I got a message saying it was incorrect, but if I entered the correct info I got Internal Server Error. I guess this is an htaccess problem, but can anyone help to correct it?