Hello there MicknMadd,
It sounds like one of your computers can see the others library and import from it, but the other does not. You've done a lot of great troubleshooting and verification already, and I would recommend steps 5-7 from the following article to help further troubleshoot:
Troubleshooting Home Sharing
http://support.apple.com/kb/TS2972
If you have a firewall enabled in your router or computer, make sure that the firewall is not blocking communication between your computers. Home Sharing uses TCP port 3689 and UDP port 5353 to communicate with shared iTunes libraries.
In addition, Apple TV and Mac computers will use port 123 to set the time automatically. Incorrect date and time on either the computer or Apple TV can cause errors for Home Sharing and connections in general.
If you are unsure whether your router has a firewall or the required ports open, test additional devices or another network to help isolate the issue. If the devices tested work on another home network, it is your router or network configuration.
For Mac OS X, you don't have to edit the port addresses, but make sure the firewall in Apple () menu > System Preferences > Security > Firewall are not set to:
- Block all incoming connections
- Allow only essential services
If you use another security/firewall software on your computer or router, follow this article or contact the manufacturer or check the documentation on how to open TCP ports 123 and 3689 as well as UDP ports 123 and 5353.
For more information on ports used by Apple products, see Well known TCP and UDP ports used by Apple software products.
If connectivity issues persist, quit and reopen iTunes on your computer. Then, quit and reopen the apps on your iOS device.
Note that Home Sharing cannot transfer or stream audiobook content purchased from Audible.com. See Audible.com for information on using their content with multiple devices.
Restart your home network router using the method recommended in documentation from the manufacturer. This may include disconnecting the power cord for thirty seconds or more.
Note: During this period, Internet services such as a VoIP-based phone will not work, and any additional routers may need to be reset in sequence.
Thank you for using Apple Support Communities.
All the very best,
Sterling