Major problem with P3P

We have a site that uses third party cookies in frames.  IE 6 was blocking
the login, so we set up P3P.  At first it did not work, but then I read a
post about including the CP code in the header and then it worked perfectly
for a couple of hours.  Then all of the sudden it stopped working, and now
cookies can no longer be used on any web page at this domain, regardless of
security settings and browser, and this is a serious problem for us.  I have
no idea what could cause this, can you help?

Kevin