Since the light fires from the transmitter's test button, it sounds like there is a bad connection in the foot of the transmitter. Make sure it is securely in the hotshoe, as well, press down when you take a photo and see if it fires. If so, then the contact in the bottom of the transmitter may have retracted. You can see if you can extract it a bit, if not, there are some possible solutions.

Long term, you should contact Customer Service for a permanent remedy.

For tomorrow, if your camera and CST have the sync cord connections (older CST's did not have this connection) you can use this to trigger the remote.

If not, you may be able to wedge something between the foot and shoe to make the connection. A small peice of gaffers tape on the top side of the foot may also help.

Green flash is power on, green triple flash is repeater mode. Red flash is transmit/receive, multi red flash is low battery

I hope this helps.

I read on the Alien Bee website that the life of the transmitter is 2 years. I have had it for a year, give or take. I was going to go ahead and order another one so that it doesn't happen again during a session.
Thanks for your help!

CST is not a "disposable" product. What you are referring to is the standby life of the battery - about two year, shorter depending on how often you fire it. Somewhere between 3 months for very heavy daily shooting and 6 months for moderate shooting. The CR2450 battery costs about $4 at Walgreens or Best Buy and takes a couple of seconds to change via its slide out tray.

The CST light should blink red when you fire it. If it does, the problem is likely in the receiver or the connection to the light. The battery powered receivers use AA batteries and have a life of about 200 on-hours. Since they automatically go to sleep if not used for an hour, that typically relates to 50-200 sessions. They also have about a two year "sleep life" when not in use.