STL File Not Showing Up on MakerBot

For my senior project, I have two parts that I need 3D printed by my teacher. I sent him the .SLT files for the printer (MakerBot Replicator 5th Generation), but when he puts the files on a USB drive and plugs it into the MakerBot, my files don't up as options to print. I tried changing the file extension to lowercase slt, didn't make a difference. The files both load just fine on MakerBot desktop to adjust settings and stuff like that. I'm doing school virtually so it's not like I can troubleshoot his end, but is there anything that I could've done to the file to make it not show up?
P.S. I read that some MakerBots must receive .makerbot or .print files, but my teacher was very adamant that the printer can take STL files, and that he has other STL files on his USB drive that are showing up when he plugs it in, just mine aren't.

try to export your files in .obj format.