Had a similar issue with my keezer a few weeks ago resulting in 3 kegs (and a few cases of bottles) freezing solid. After I got a handle on the temp, all my beer was pouring as nothing but foam. I suspect that the temp drop allowed additional CO2 to be absorbed by the beer as it cooled and finally froze, resulting in super-over-carbonated beer once it warmed back up again.
Working on this assumption, I shut down the gas to the kegs and then purged excess CO2 over the course of several days until the beer was completely flat. Turned the gas back on, waited a few days for it to carb back up to the proper level, and was rewarded with beer that once again poured properly and had the correct amount of carbonation.
