Hi,
possible bug. Reproduce scenario:
1) My copper mine had got depleted
2) I tore it down
3) I got a free settler back, but no building licence - it stayed at 0
4) Now I can't build the mine again, because I have no spare building licence
I tried to relog and clean cache & cookies, no luck. Using last Chrome (15.0.874.121) on Win7.
Hope this helps,
Troubic