K8090 issue - unable to connect to com port


I’m using several K8090 relay cards in a retail application across 7 outlets and this has been in place for over a year now. However, we occasionally get an issue where the pc is seemingly unable to connect to the com port anymore. My application is written in VBA (MS Access) and doesn’t give any errors when this problem occurs, it’s just that nothing happens on the relay board when the appropriate instructions are sent.

The device is always correctly listed in device manager and when I run the Velleman demo software, it always correctly shows the com port but clicking the connect button gives the error ‘Failed to Connect. The system cannot find the file specified’. Additionally, any on-board timers previously set always correctly complete and switch off at the correct time.

A reboot solves this problem every time. We can go weeks without it happening but today for example, it’s happened three times in the last couple of hours which is frustrating. Any thoughts or ideas on what causes this please; no other pc issues are evident (i.e. other usb devices seem ok) and it happens on different pcs in different premises?