lawn tractor- won't move

This is weird but I have a Sears lawn/garden tractor I've had for almost 3 years.
The other day, I was using it-then I decided I should check the tire pressure. I stopped it, checked the tire pressure, then started the engine and it wouldn't move! I could hear the engine trying- it made a sound as if it's struggling, but can't, as if it were up against a wall.
So, a friend nearby drives his over so I can use it while I get my fixed. I was going to use his, but didn't have time so I rode his back to his house a hundred yards down the road. I parked it in his driveway- he got in and drove it to his shed- parked it- opened the doors of his shed- then got on the tractor, started it- and IT WON'T MOVE.
So, he's a lot smarter than I am when it comes to mechanics. He said, "when you parked it- you didn't have the break on- and you're not supposed to turn the engine off without first engaging the break- you must have done the same with your mower too- and so it's your incorrect way of parking the mower that caused some problem with the transmission or break system or clutch on both machines."
A guy down the road fixes lawn equipment and snow blowers- I asked him and he said it's unlikely not engaging the break before turning off the engine could cause the problem. He's too busy to take in the machines at this time without a long wait- so I called Sears- and they'll send their guy over next week.
I do notice that my manual suggests engaging the break before turning off the engine- but I just thought it was for safety reasons, in case the machine was on a hill- it might roll.
My machine is a fully automatic with a pedal for forward and a pedal for reverse. My neighbor's is different- no pedals so he has to use a stick to control speed and direction.
So, was it my incorrectly turning off the engine without the break engaged that has somehow damaged both machines? My machine only has 73 hours on it so I doubt that the drive belt is broken.
I suppose that if you turn off the engine without engaging the break and thus disengaging the clutch- perhaps the clutch can be damaged? Is that like turning off a car engine with a standard transmission without disengaging the clutch? I dunno, I don't understand mechanics.
Any suggestion?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Not putting on the brake before shutdown didn't hurt anything. It's like you said, a safety feature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.