Maybe clear the Cache and Optimize Tables.
A few pilots in my Va use kAcars free and they dont get this problem, same with Xacars, no problems, I flew 4 flights today with FSAcars and the map updated each time and showed the correct amount of pilots flying at once.
One suggestion though, go into your skin folder, if the acarsmap.tpl is in there, delete it, ive noticed sometimes that can cause the problem.
Oh and delete and other files in there to do with the acars files etc.
Hope this helps you.