Edgeport/2 - unable to open COM4. Please check your port settings

Problem: Edgeport/2 USB to Serial installed on Windows7 Professional system.
Serial Port - 1 = (Com4) , Serial Port - 2 = (Com5).

Driver Provider: Digi International

Driver Date: 5/5/2010

Driver =

Properties reports - device is working properly.

Port Settings = 4800, 8, None, 1, Flow Control = None

Attached to Edgeport is XStream-PKG wireless modem with baud set to same as above.

Using HyperTerminal for communications.

After rebooting PC HyperTerminal reports following message:

Unable to open COM4. Please check your port settings.

I’ve check everything which seems to be ok. I have to disable device, reboot, then enable device. then all is works again.
I have also gone through unistalling and reinstalling which also fixes the problem.

Does anyone know if there is a driver problem with Window7? any other ideas would be helpful.