[Lara]

In the test environment for Valdrdomr:

I have an army in a hex co-joined but can not occupy it.  The submit button doesn't work.

[Kutara]

From my own testing, your troops have to sit there for a week before the occupy command will take. I assumed it was intentional.

[Lara]

I have just tested moving an army, running end of turn and then occupy and it works as intended, archiving this and assuming this was a very old bug.