Login Script Problem

i have created a login script that enables my costomours to login into there cPanel,web mail and if there a reseller WHM.
But when i test the script on the webserver its dosnt work on some pages, on the pages that dont work i get this error message

Method Not AllowedThe requested method POST is not allowed for the URL /index.htm.

Apache/1.3.34 Server at http://forums.xisto.com/no_longer_exists/ Port 80

and i know its nothing to do with the frontpage server extentions, and what gets me is that it works on some pages but not others. Ive tried everything in my knowlage to get it working and it dosnt, so if anyone knows how to solve this it would be greatly appriciated.