ASP.NET Class Library not hitting break points

I have an ASP.NET web aplication using vs2008. It used to let me hit my break points but for some unknown reason in this site it won’t let me hit them any more.
I have set everything to debug and re built about a million times and everything else but can’t seem to hit that damn break point!!! Break points work for the site but not the class libraries I add in, but they used to!!