Detect what software is blocking connections

Hello all!

If this is offtopic, please advise of a better newsgroup, I thought
this may be the right one.

Our customers download and install our client/server based software on
their computer. Many of our customers use Norton Internet Security and
other types of software that block ours from connecting to the
Internet. Sometimes the users don't know to click "Allow" and they
block it then call us wanting to know why it's not working.

My problem is that on some computers, we can find no software that is
blocking connections but it is obviously happening. My question is does

anyone know of any software out there that will tell you what program
in memory is blocking network connections or acting as a firewall?

Thanks so much!