I'm having the same problem as well. I just opened tier 3 not a few minutes ago, bought my doffs fresh from the exchange and can't seem to donate them either. I keep going over everything to make sure I have the right doffs and I'm sure I do but still nothing.
Don't have any fleet doffs, so that's not a problem. And I can't see why it would require fleet doffs since some people aren't in fleets and that would keep them from completing the project in the first place. Unless you can buy fleet doffs on the exchange? Haven't been in a fleet long or looked for doffs in awhile, so *shrug*. The description says any uncommon green engineering or operations duty officers. I bought them off the exchange, just random engineering and operations doffs.