Exchange question

I am wondering what the problem here is.. We run Exch 2003 and everything here locally is great. The problem is when our sales guys access our web access. They can access the web mail okay and even get to their local inbox, when they attempt to acess the public folders to xfer files and such it says forbidden and doesn’t allow that.. I personally think it’s a permission issue but I have searched and searched and not able to find soloution.. HELP PLS