Can't share file after program "update"

Hello,

I'm new to networking & have encountered a problem.

PC 1 has Program X running on it. PC 1 also has router & wireless broadband
attached. I was able to successfully configure sharing so that I could run
Program X from PC2 through network.

Program X was a few years old, & rather than issuing updates, Program X
required a new software download & is now Program X2. I can run it from PC1
on which it is installed, but I can't run it from PC 2 as I did before when
it was just Program X. Since I ran it before new version, I would think I
have the sharing correct. In fact Program X2 has a direct email executable
file, & I can run that from PC2.

I've tried adding Program X2 to the exceptions in the Windows Firewall, &
I've tried disabling the Firewall, but neither works.

Any suggestions? Does this sound like something I've missed, or some quirk
in Program X2?

Thanks in advance