Peter Scholz wrote:
You have KNOTT brake.

I have a KNOTT trailer, which I presume has KNOTT brakes as well.
Sometimes after standing over a humid winter one or both brakes locks
on. The solution is a hammer (I now keep a 4 lb club hammer in the
trailer). Jack up the offending wheel, give the head of each wheel nut a
firm tap, rock the wheel, repeat until it frees.

I've had the brakes checked out by a garage (auto repair shop in US?)
and all is fine, but this still happens. My guess is that somewhere in
the brake mechanism is a narrow clearance which tends to lock up with
corrosion.

The wheel won't free up if I don't jack it off the ground (well, not
without hitting it harder than I care to), but jacked up it usually
frees before I've tapped every wheel nut. Obviously, hit the nuts
square-on so as not to round them over.