This fix is previously posted by one of the creators of WE mod, @Hizkiyahu on WE's old, abandoned mod (WE: Complete Edition) workshop page. I just copy-pasted what he said to here, just so people can have easier access for it. And no worries, this works on between ACT and WE:R as well.

Originally posted by Hizkiyahu:

OK I think I have a fix here. Edit ACT.sql in the ACT mod and change
INSERT INTO Units_XP2
(UnitType, CanEarnExperience, CanFormMilitaryFormation)
VALUES ('UNIT_AIRCRAFT_CARRIER', 0, 0);

to

INSERT OR REPLACE INTO Units_XP2
(UnitType, CanEarnExperience, CanFormMilitaryFormation)
VALUES ('UNIT_AIRCRAFT_CARRIER', 0, 0);

then edit ACTweak.modinfo and add

<Properties>
<LoadOrder>99900</LoadOrder>
</Properties>

to

<UpdateDatabase id="NewAction">
***** INSERT HERE *****
<File>ACT.sql</File>
</UpdateDatabase>

Then remove reference to ACT_MOD.sql as it is not needed.

Upgrades will work again and logs will be clean.

And also if you want the restriction of ACT applies for Supercarrier (no exp gain + can't form fleet/armada) as well, just do this:

Originally posted by Dante.Enoshima:

Edit ACT.sql in the ACT mod and add:
('UNIT_SUPERCARRIER', 0, 0);

to

INSERT OR REPLACE INTO Units_XP2
(UnitType, CanEarnExperience, CanFormMilitaryFormation)
VALUES
('UNIT_AIRCRAFT_CARRIER', 0, 0),*
-----INSERT--HERE------

* = At the end of that line, it's supposed to be semicolon. Change that semicolon to comma if you decided to do what the above said, to avoid errors.