VPN Access Problem

I have PIX 501 with 10 user license. My LAN has been connected to our Head Office LAN through PIX. In my office only few people (around 8 or 9) are only able to access VPN simultaneously. Is this due to the licensing? I heard that licensing issue will not be happen in LAN-to-LAN connectivity. Is that true? One holiday I came to office and started connecting the systems. I was able to connect around 15 systems.

Anyone can help in this??

Thanks in advance.

Sktopdog