Both PC's have the latest iTunes installed. PC (A) can "see" that there is a shared library "B library" but attempts to connect to it return this error message:

The shared library "{Username}'s Library" is not responding (-3259)
Check that any firewall software running on either the shared
computer or this computer has been set to allow communication
on port 3689.

however the reverse works fine. e.g. PC (B) can "see" shared library "A library" and can access all content.

Notes:

• Both PC's have Home Sharing enabled (turned off/on several times to verify).
• Both PC's have Windows Firewall turned on, but in the exceptions tab, iTunes is allowed, and Port 3689 is also added as a firewall exception (just in case)
• Both iTunes accounts have been "authorized" on both PC's
• Both PC's connect via LAN via D-Link DIR-615 router. In the advanced application rules, iTunes has also been added to allow traffic on port 3689 un-hindered.

Is there any other magical setting/configuration option that I should be aware of and set in order to get this to work? I could care less about sharing apps etc. I just want the music sharing to work.

Update: Solved!

• It turns out on PC (B) there were multiple accounts set up. 1 of the accounts had the checkbox checked under the windows firewall "On" option which states "No exceptions" thus even though it was added to the exception list on the main user account, this other account was blocking access.