HP SCANJET ENTERPRISE 7500

I have an HP Scanjet Enterprise 7500 scanner, for several years, it has always worked perfectly, until about 40 days ago, when out of nowhere, when placing the sheet of paper at the top (tray) the green light turns on in the normal tray, but when giving the command to scan, it "seems" that it is going to pull the paper, enters the tray 1 centimeter and stops, appearing the message below.
"The scanner's document feeder has a jam. Resolve the conjection, reload the pages, and try scanning again.
I've already taken it to two stores that repair printers and scanners and both said they don't understand how you can say that there is paper in the feeder/tray, they have already disassembled the scanner and cleaned all the parts and the problem persists. On glass it works perfectly, but on the tray there is no way, does anyone know what it can be?

Nilson

Thank.

Sorry for my English, I used Google, my language is Portuguese.