I don't know whether you are talking about the 396T or XT, but there are certain memory limitations.
The following are for the T model:
Systems: 200 max
Groups: 20 per system
Channels: up to 2500
Channels per Trunked System: up to 200
and for the XT:
Systems 500
Sites Total 1,000
Sites/System 256
Channel Groups per System 20
Channels+System Frequencies 25,000
Channels per conventional system 1000
Channels per trunked system 500
Trunk Frequencies per Site 500-1000 (depending on total TGIDs stored in the system)
Bear in mind that a trunked system control channel frequency counts in the number of channels per trunked system. So if you exceed 200/500 you'll get a memory error.
Also you could be below 20 groups per system, but if you attempt to program more than 200/500 total number of channels, that will lead to a error condition. (For example 11 channels in each of the 20 groups would be 220 channels, or 20 more than allowed in the T model).