On various Linux distributions, and most notably RedHat Enterprise Linux 5 and similar, the default iptables rules mean that all ports are closed. Therefore, lmgrd will not be able to start (or be seen to outside computers).
To fix this, i.e. to run a license server on a RHEL 5 machine or any similar distro with iptables, you must open the relevant ports. Detailed instructions can be found here: http://www.cyberciti.biz/faq/howto-rhel-linux-open-port-using-iptables/
For lmgrd, you need to open first 27000 (or 27001 or whatever you choose as the lmgrd port; you need to enter this number in the license file, and use the same port number from the client computer), plus a port for the vendor daemon. Now, this port is random, unless you specify it explicitly. To do this, add a port specification to the VENDOR line in the license file, like so:
VENDOR atomist port=34564
Then, open this port too. The port number is quite arbitrary, just make sure it is not used by some standard services. Choosing it quite large, in the 30000 range, is quite safe, most services work in the 2000-7000 range.