Error 403

I keep getting error 403 when I try to view documents that require plug-ins
to view them as in .doc & .pdf files. I have tried using other browsers and
it still happens. I can't quite put my finger on when it happened, but it
seems to have co-incided with the last big batch of XP security updates about
a month ago. I have tried disableing my fire-wall and that has no effect. I
use no pop-up blockers download accelerators or anything else. If I try and
open up a file already on my pc by typing c:\desktop\help.pdf or other, that
works fine from within IE but not if I try to open a web page .pdf or .doc?

Has anybody else experienced this?

XP Home SP2
IE 6.0