What would cause the driver's side front wheel to lock up?

squallingly?

with a tow truck genius. if you don't know what squall means, go look it up in the dictionary

If there is no bearing problem then you need to look at the brakes. Was the rotor hot when this happened? It should have been blazing hot if the brakes were being applied on that side. This can be caused by a sticking caliper that is dragging and getting hot, or in some cases I've seen, a malfunction in the ABS system, sometimes caused by an air bubble, though I suspect your caliper simply got stuck and dragged till heat expansion seized the wheel.

How about a dry differential?... That just might account for this problem!!... You know...run without any lube in it!!!!!!!!!!! Car owner; .. It's not really "genius" ... just experence!! ... But thanks anyway.....

Remember the older Toyota's that had the sae 80 w 90 gear oil in the differential section of the transaxle??... That nobody ever checks.... Until the wheel locks up!!!!!!!!.. Spider gears still turn ..(as in jack it up and wheel will turn) .. BUT the ring gear and pinion DONT... when it's on the ground!!!!

that was the first thing i thought, but the bearing was perfect

This vehicle has a seperate differential that has its own lubrication or gear oil!.. It does not get lube from the transmission!!!!.... Has that been checked to see it it is out of lube???? It has a check/fill plug on the differential part of the transaxle assembly, hard to see unless on a lift... That needs to be checked as it will surely cause this trouble!!!!!!!