We're having a .net web-application having it's cache policy set to
"NO-Cache".

MSDN Details:
http://msdn.microsoft.com/library/de...classtopic.asp
[and]
http://msdn.microsoft.com/library/de...CacheTopic.asp

This is important for our site, as no result of a web-form post should
be cached.

Before Windows XP Service Pack 2 a correct error Message "Warning:
Page expired..." was shown. The customers understood!

After installing SP2 the error Message "Page cannot be displayed" is
shown. It turned out that the IE Option "Show HTTP Friendly error
message" has to be turned off to get the old error message.

As we have a lot of traffic, people are calling/writing emails
thinking our site has an error.

What is the best solution? On the one hand we need no cache, but on
the other hand we can't explain every customer how to deactivate this
IE-option?

Thanks for ideas!