Thanks everybody for help. I checked this issue on other notebooks: Toshiba Satellite C55A an Lenovo IdeaPad S210 Touch. Both with Windows 8.1 64bit. This problem is concerned on every Windows 8.1 64bit. This method helped:
Please disconnect PLC from USB cable.
Disable UAC at your computer.
Go to directory C:\Program Files (x86)\Common Files\Unitronics\USB Driver
Run VCP_V1.3.1_Setup_x64.exe file.
When installation finished – connect PLC to PC and leave it until it install and then update driver. Sometime it will take tens of minutes.
Check in Device Manager if installed driver is OK – appears under Ports. Then you can use corresponding COM port. Port number should be between 1 and 16.
If it does not works – tray other resources (from web):
http://www.navmantech.com/aumarketing/EDM/Support/Magellan/VCP_V1.3.1_Setup.exe
http://www.navmantech.com/aumarketing/EDM/Support/Magellan/VCP_V1.3.1_Setup_x64.exe