HotSpot active users on level 4 are with limitation of 200

What does it meas:
a) on the NAS device (level 4) only 200 active - I believe this is the one
b) on the other device (level 4) with UserManager only 200 active

cause I have a small hotspot system with mikrotik 951ui and free radius server on FreeBSD, and I would like to go with UserManager
what is going on if 202 users try to log in?

I don't understand what you mean by NAS device.

1. Level4 allows only 200 active hostpot users. when user #201 tries to log in, he will not be able. he must wait until somebody logs out first
2. If you use User Manager, it also has limits: level4 allows only 20 active users. you need Level6 to have no limit on Hotspot and on User Manager active sessions

http://wiki.mikrotik.com/wiki/Manual:License