Losing session information

Dear List,

We moved our website (www.ptgrey.com) to a new server a month or two ago.
We just started noticing that we are having problems, something to do with
session info. We run an ASP FAQ package (PensaFAQ) as well as a couple
custom-rolled ASP apps and these let staff login to add items to the FAQ and
such. However, when staff try to login, they sometimes get kicked out right
away with a message from the software that "your session has timed out".
Then if they try again (or if they get in in the first place), they can work
for 5-15 minutes before getting kicked out with a similar notice.

I've had the software vendor for PensaFAQ look at our site / code and they
did not identify anything in the ASP code (not surprising since both their
code and ours are affected). I have also followed many tutorials on
managing session timeouts including worker process recycling and session
length in IIS manager as well as setting session timeouts in the Web.config.
None of which have had any affect.

I have even put a dump of all the Servervariables on a page and the is not
apparent difference from one page load to the next in this output:

<%
For each item in Request.Servervariables
tempvalue=Request.Servervariables(item)
Response.write item & "=" & tempvalue
Response.write "
"
Next
%>

The only thing that changes is that the session variable (pw_prg_Username)
comes up with my username sometimes and blank other times when refreshing
the page.

I have tried the "standard" troubleshooting stuff: Restarting IIS and
rebooting the server (it's a VPS). Neither IIS nor ASP are my strong suit
so I really need all the help I can get! Any troubleshooting advice or
pointers in the right direction would be greatly appreciated!

Thanks!
Dominic Lepiane