We have identified a problem with the PlayerIds used to identify players in the multiplayer games. The problem is that while PlayerIds are unique for individual products, the same PlayerId can be used for a different product and players with different products can play together on the same servers.
Products currently conflicting are:
A2 / A2Free
A2OA / ArmA 2: Reinforcements / ArmA X Anniversary Edition
The conflict for the Operation Arrowhead family of products was solved by changing PlayerId for all players using ArmA 2: Reinforcements or ArmA X Anniversary Edition. The users ArmA 2: Operation Arrowhead will find their PlayerIds unchanged. We are sorry for any inconvenience caused, but unfortunately such conflict cannot be solved in a 100 % backwards compatible way.
The solution is implemented in build 94002 and will be available as a public beta first, and a stable patch later.