error when reply to a post

Hello,

I have created a real simple web using only the Discussion Web Site Wizard.

I then published it to my host site, which is actually my ISP (Comcast.)

Users can post an new post, they can search and get the results, they can
see the table of contsnts - all without problems.

However, if someone replies to a pot, they get FORBIDEN: You don't have
permission to access /~johndoe/_vti_bin/shtml.exe/Discussion_post.htm on
this server.

This is odd to new since I can create a new post w/o problems.

Can someone please advise, offer your thoughts?

Thank you