Recently completed building my New Prusa i3 MK2, already have an i3, and after running a few prints through the new printer via the SD card, I decided to download the Windows version 1.7.5 package so that I could talk to my printer via a PC.
The package loaded correctly, installed Slic3r, and Printrun as well, checked my Device Manager Com port listing and noted that my new printer show up as "Original Prusa i3 MK2(COM7)". Started Prinrun, and then attempted to connect the my new device at 250000.
Received the following error message in the Printrun Console window:-
[ERROR] Could not connect to COM7 at baudrate 250000:
Serial error: could not open port COM7: [Error 5] Access is denied.
Then attempted to try connecting via every COM port available on my PC, as well as at every speed listed, while still getting the same type of error message.
The only way that I have so far been able to talk to my new printer via a PC is to go into the Device Manager screen, right-click on my listed printer, and uninstall the driver. To my amazement after a reboot I found that Windows 10 had installed a driver, for my still connected printer, and it was not the Prusa one. Tried connecting to my printer via Printrun and it worked, but only at the 115200 baud rate, but at least it worked.
Prusa support tell me that I appear to be the ONLY person to ever have this problem, so I'm looking to see if other users have had any issues