LoopBe1 uses "feedback detection" that can not be disabled - as far as I remember... this checks for higher speed than classic midi (31.25 kBps) which can easily occur when data flows just inside a PC... I remember as well that this drove me nuts...
The payware LoopBe has an option to disable feedback detection...
...but my recommendation is trying free
loopMidi from Tobias Erichsen
http://www.tobias-erichsen.de/Software.html
It is easy to use and all can be set up dynamically - no reboot on changes. You just need to install AppleBonjour services for PC which is free too and can be downloaded from Apple.