This has happened to me on occasion in the past few builds. I enter tactical combat and then start to do my thing but suddenly I can't attack or move any units. End turn button doesn't work either. If I hit the auto-resolve button from within tactical combat it will end successfully and go back to the strategic map. I tried to duplicate the issue by loading the prior save, reentering the same combat, and performing the same steps. I was unable to duplicate it. I peeked at the debug and nothing in there to help. I wish I had more info besides the save and printscreens to help debug this but alas, it seems to be an elusive little bugger. Please note that the results on the victory printscreen do not match the actuals I experienced within the tactical combat. Maybe that will help debug?
At any rate here's the information right before it happened:
Left Fanboy - used 1 action to attack, was hit for 2 on counter, then I switched to right Fanboy to spread out the counter dmg

Right Fanboy - used 1 action to attack, was hit for 2 on counter, tried to switch back to Left Fanboy. After clicking on Left Fanboy is when the combat "froze" where it would not allow the units to attack or move.

Frogboy - haven't used any action points yet because the combat is frozen

Bandit - note he has used 2 of 3 action points countering both Fanboys and has 24/36 hp remaining

At this point I hit auto-resolve (after experiencing this before I knew it would work). Below is the Victory screen. PLEASE NOTE: The victory screen shows that Frogboy took 2 dmg, not 2 dmg each to both Fanboys. As you can see from the above printscreens, both Fanboys had 2 dmg and Frogboy had none. The results of the victory screen do not match the stats before combat froze. Maybe that will help track this down?

[Edit] I got a bitchin' ring!