You could try port forwarding your Linksys for that specific computer. Port forwarding is computer specific (internal ip network based.) However that might affect the other computers if they are running of UPnP & you need to switch over to port forwarding. May need to port forward each of those also (a different port for each computer.)

That model router is reknown for not working well with p2p in UPnP mode. However if it's working well for you with the other computers then I cannot argue. I presume you are interfacing them via ethernet cable rather than wirelessly. Wireless for this model router is generally not super reliable when large bandwidth is used. (symptoms of wireless unreliability: bandwidth drops ... sometimes connection stops. This model router does not handle large amounts of messages well when not port forwarded.)
See my previous post link.