Strange RPC/HTTP behavior

This is likely a simple question for someone but I just hope I can get
some information on ti to deliver to the customer. We have implemented
ISA2k4 and are publishing our OWA. I am using the same rule to publish
out OMA and RPC by just allowing a few more directories. The error code
redirection changes it to HTTPS and using the IISSTART redirector I get
OWA users to /Exchange.....working well.

The big mystery I am having, and wondering if there is anything is then
setup I should look at or something that might point me alonjg.......is
RPC clients. RPC over HTTPs works well, clients connect, mail comes in,
mail goes out - the only problem comes in with the manual (F9) synch.
The sending works fine but the recieving never happens.

I know there are scripts to disable that button but the customer would
really like to keep it if possible. I have ruled out the client
workstation I am testing with

I did see some errors that are referenced on this site about https
connect failures with HTTP status of 64 and another one. The suggestion
was enablePMTUDiscovery....anyone think this might work in my case?

.