Uploading on EV3 doesn't work

If I try to upload my programm on my USB-connected EV3, the upload gets stuck after around 20%.

Output in the Window "Uploading to EV3..." is:

Preprocessing start.lms [DONE]
Generating rbf: C:\Users\john\AppData\Local\Temp\ev3starter5161276984488606014

Then it gets stuck.