No connection with Pronterface

I’m using a Windows 7 operating system. I’ve just downloaded the driver successfully. Once I got the Pronterface program up and running, it showed a COM7 available, but will just say “Connecting…” forever. I close the program and open the pronterface.exe text file and it says:

serial.serialutil.SerialException: could not open port COM7: [Error 5] Access is denied.

Did I just forget a step in this set up process?


Try either turning UAC off, or running Prointerface in adminstrator mode (right click, run as administrator) and see if that does the trick

If you don’t mind, try checking with a new user account in Windows, to see if anything else you may have installed locally is interferring with comport access.

Create a new user account in Windows. A guide is available here for Windows 8: For Windows 7:

Once the new user account has been created, download the TAZ driver from here: and install the driver using this guide: and Printrun from here:

Once the driver has been installed under the new account, reboot both the computer and the printer. Sign into the new account and connect the TAZ 3D printer. Run Pronterface and attempt to connect.

Have you been able to connect to the 3D printer through USB previously? If this is the first time that you’ve tried, contact us at with your order number, 3D printer serial number (found on the rear of the printer, at the base of the electronics enclosure). Screen shots of your device manager screen showing the RAMBo line entry and the properties tab will help identify were the connection is failing.