UPDATE: I made a video illustrating how to fix this problem yourself if your lock is not covered by Baldwin’s lifetime warranty or you don’t care about it. This weekend three separate customers called about their Baldwin locks not working from the outside (though in two of the cases, they worked from the inside). In two of these cases it was because of stripped gears made of cheap die-cast metal. The replacement part is 5399-003-G for many of these, which are usually from Baldwin’s “Image” line. Baldwin made some of these parts kind of weak so they released a conversion kit to replace these parts that are known to fail.
You can take the piece apart that the thumblatch interfaces with. It has a thin piece of metal covering some gears. The thin piece of metal is held on with either screws or little metal tabs that must be bent back. Once you have it off you have to turn the gears 180 degrees and then put it all back together correctly. And then alleviate the issue which caused the problem in the first place.
The important thing to know about these Baldwin parts that frequently fail is that they are covered under a lifetime warranty. The other important thing to know about them is that you must alleviate the issue that caused them to fail in the first place. After the part is replaced, make sure that it is really easy to use the thumblatch. If it is difficult to use, there will be too much pressure on the gears in the lock. This may be because the strike is installed too close to weatherstripping so that the latch binds against the strike, or it may be because the lock was installed slightly off center so that there is undue pressure on the latch. Baldwin hardware runs on the heavy side, and if you screw it in where it hangs it will be pulling the latch down from where it should rest. That translates to premature failure.
If you are handy with a screwdriver, take your broken thumblatch off the door and take it to a Baldwin dealer. They can supply you with a replacement part free of charge due to the lifetime guarantee from Baldwin. If you live somewhere more rural or don’t want to deal with it all call 1-800-437-7448 and describe the problem. Baldwin will mail the parts out to you. You can then hire somebody like me to swap the broken parts.
Good luck with your lock!