htaccess problem

I really dont know what the hell is going on.
The problem is hard to explain. I will make this as short as possible. I have fast secure contact form installed. I also have a .htaccess file uploaded to my root. the htaccess has 2 features: index.php to root, and non-www to www.

when the htaccess file exists, my log in and password for the fast secure contact form admin area dont work. It won't let me in.
so to make any changes to my forms, I have to delete the htaccess file, at which point my username and password for fast secure contact form work again. then I log in, make my changes, log out. Then I reupload the htaccess file.

I dont get this shit. Why the hell is there a conflict?
FYI, I have stablehost and I have multiple addon domains hosted with them. maybe that's where the problem is, I dont know.

Maybe you messed up your .htaccess file somehow.

That thing, fast secure contact form, is a plugin for WP?
So, you use wordpress? Do you use permalinks?
Post your .htaccess file?