permalink structure causing redirect problems

I put in /%postname%/ as a permalink structure on all of my wp blogs and then copied the rewrite rules that were generated into my htaccess file as directed.

I’ve found that if someone tries to go to a nonexistent page on my server, e.g., http://www.mydomain.com/nopage.htm instead of getting page cannot be displayed, the first wp blog whose rewrite rules are in htaccess is displayed but with no posts.

I asked my host and they said this is being caused by the wp permalink structure rewrite rules in htaccess … but if I take out the rewrite rules then I won’t have the permalink structure.

Any advice what to do?