Hi Shaun,
I am no expert on X-plane and this by no means is an official answer but I offer the following information.
1. Version 10.50B is a beta version. The letter "B" signifys this. Currently B7 or B8 is the latest version and seeking advice on faults detected by those who are testing the software. When there appears to be no more perceived problems, 10.50 will be officially released. My suggestion would be to go back to 10.45 and use the same versions. There are others in this forum to others on how to back track from beta to the official release software ie 10.45
2. In response to your "multiplayer" question I cannot remember the answer provided to others asking the same question in this forum. If you click on the orange tag "multiplayer" shown in your original question it will bring up all the questions asked with answers provided mostly from jroberts from Laminar Research. These earlier questions should provide the answer you are seeking.
Hope this helps.
Glenn