Re: 4 wheel low lock-out (or lock-in)???
Not sure how familiar you are with 4WD but did you by any chance make a sharp turn just before you tried to disengage 4Lo? Sharp turns on high traction surfaces can bind up the driveline making it difficult to shift. Driving for awhile may relieve the binding.
Nothing wrong with asking the dealer about it, however. He may ask the same question.
2011 WK2 Overland Mineral Gray/Black, Advanced warning, V8; 2009 KK Rocky Mtn V6; 2000 WJ Laredo I6; 1979 CJ7 I6... green... miles of smiles :)