User licence is different to ISAKMP Peer licence numbers. Do a "sho ver" on your PIX and check the values as indicated below:
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Licensed Features:
Failover: Disabled
VPN-DES: Enabled
VPN-3DES: Enabled
Maximum Interfaces: 2
Cut-through Proxy: Enabled
Guards: Enabled
Websense: Enabled
Inside Hosts: 10
Throughput: Limited
ISAKMP peers: 5
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If you only have 3 ISAKMP Peers then you'll only be able to build 3 tunnels to 3 different hosts (that includes LAN-to-LAN and client tunnels).
As for what constitutes an "inside host", it is:
- has sent or received traffic through the PIX in the last xlate timeout seconds (five minutes with the 501 default config).
- has a UDP or TCP connection
- has a NAT session
- has a user authentication session
So basically a PC sending traffic through the PIX is an "inside host". That one PC can have any number of connections and translations, that number doesn't matter.