When I try to to open a COM port in Docklight, I receive an error message “The communication port COMxxx could not be opened. Windows Error #5 – Access is denied” or simular. I carefully checked that no other application is using this COM port. I also noticed the error only appears sometimes, or using a certain Docklight version. The Windows Hyperterminal software seems to be fine, for example.

Applies to: Docklight / Docklight Scripting (all versions), Article ID: dl_prb028

If Docklight returns an “Access is denied” error for no obvious reason, there is most likely another application installed and working in the background, which opens or otherwise accesses this COM port. PDA sync tools like Microsoft ActiveSync are examples for such software.

To resolve the problem, check carefully, if there is a software on your PC which is started automatically and communicates to GPS equipment, phones or other communication accessories. Sometimes there is no other solution than to deactivate the sync tool, or run Docklight on a different computer.

Sometimes the problem is specific to a certain serial driver, e.g. for FTDI-based USB/Serial equipment, and using another COM port on this PC, or a different brand of USB/Serial converter, can resolve the problem. Another reason might be a USB / virtual device driver that simply does not allow to set the classic serial communication parameters (baud rate, ..) when opening the COM port.

See the troubleshooting article below for details on this issue.

Docklight Troubleshooting – When trying to open a COM port, I receive an error