i got a problem with nw6 sp3, NBM 3.7 sp2 with fieldpatch c.

i am hosting some websites on a win2k server (running apache 2.047,
mysql 3.23, php 4.3) behind the boardermanager. i am using the
reverseproxy to "make" some speed.

my problem:
after some days the website doesnt show up any more. by tipping the
url in the browser a window comes up saying "please download".
i downloaded the file and looked at it, there is nothing usefull in it
just trash.

to me it looks like a cache problem, but i cant find any probs.
i changed the server (new/other hardware), installed netware and nbm
again, changed rules, viruspat loaded, changed log-file
..... the prob is still there.

any suggestions

thanks for your help
ps: i know nw6.5 with apache/php/mysql...