urgent: cache problem

[z. f.]

i as trying to cache an asp.net page.
i want the cache to be only on the server. client caching is not interesting me at this time.
for some reason i can't get the page output to be cached correctly.

i use the
<%@ OutputCache Duration=120 VaryByParam=none Location=Server %>

i want the page to give the SAME output for different parameters.
but it gives me different output for different parameters.

WHY???

is there some restrictions on setting the Response.ExpiresAbsolute if the page it cached?

does the cache includes HTTP header changes, or just the output HTML?

TIA,z.