Paint over it with KILZ alcohol-based stain-killing primer. it's the stuff that says to use alcohol as a clean-up. Used for smoke and water damage sealing.

Latex paint WILL support mold growth, and sometimes being opened to add the colorant lets the spores in. It's not a problem if you paint soon, but a couple of years

It's also possible that the paint had started to break down (chemically) from the temperatures in the garage, and the byproducts of it are the source3 of the odor.

KILZ is oil based. BIN is the shellac based (alcohol) stuff. Both stink.

The only time I've dealt with the musty smell after painting is when it's humid out. The drying paint is going to give up water vapor anyway, so it may add to that.

Since it's in a garage, open everything up and let it dry out real good, and see if that helps.

I routenly repaint with paint that is several years old (like 5-6 years even) and have never had problems with it being musty. However some manufactures use cheaper cans now and I've ended up with problems because of that.

I will add too, I never store paint in the garage, it's always been in a relativly climate contolled area - my basement that does not get real hot or cold no matter what time of year.

Paint that has been stored where it is subject to exreme temperatures can have all sorts of problems. I won't use paint that I know was allowed to freeze.

The SW salesman told me that two years shelf life is well within acceptable time frames for selling unopened stock.