zalmi, your symptoms sound near exactly to what I had experienced with my Tyros. Following a USB hardware replacement/upgrade by Yamaha Corp, all Tyros USB flakey connectivity problems have been resolved. The USB connection is now functioning reliably ALL THE TIME. I recommend contacting Yamaha Europe about this as they now have an official hardware fix for this. It is covered under warranty.

Here's a link to one of many threads where I discussed the problem, as well as finally . . . the solution : http://www.synthzone.com/ubbs/Forum37/HTML/008856.html

Scott