Another bug here, though it's slightly more difficult to reproduce than others i've reported.
At the end of Chapter II I've had issues sieging the fortress Atuatuca.
Basically it'll let you have one unit begin sieging, but as soon as that unit breaks off the siege,
further attempts to siege the fortress display a 'insufficient space' message.
I've tried with multiple units, ballista, heavily dimished Legions, etc.
Upon reloading a saved game the issue temporarily fixes itself; you're able to select one or more units and siege the city again.
But as soon as the siege is cut short, this error happens again.
To reproduce this bug;
Load the saved game, you will see two Legions.
Select one and tell them to siege the fortress Atuatuca northeast of their position.
They will siege for a bit, then be driven off by the fortresses defenders.
Then select the second Legion and attempt to siege Atuatuca.
You will/should get the insufficient space message.
And this message will/should happen for all units making Atuatuca unable to be captured,
unless saving and reloading.