I post this in case someone else runs into a similar problem.
I just had my main computer hardware upgraded - new motherboard, CPU and RAM. Of course I had to reinstall all my programs, device drivers, restore files and customizations, email settings, etc, etc. Everything was working fine except my USB / Firewire Microtek Scanmaker i900 scanner. I've been in the throes of deep depression and withdrawal without my scanner - after all, what does someone like me do without a scanner?
At first, I actually did install the drivers improperly. With the help of Microtek, I did a "clean" install of the drivers to get back to base one. After that new install (of many) - I successfully opened my scanner software and clicked the "overview" button only to get a message:
System 31, a device attached to the system is not functioning.
This is a Microsoft message, but a search in their knowledge based did not reveal anything of help.
My system has 4 USB ports on the motherboard and 4 on a separate PCI card. I was plugged into the PCI card USB port.
Microtek and I were at our wits end. In searching the web, I did see a post by someone saying to plug directly into the motherboard USB port instead of through a hub - but, in my mind, I didn't have a hub, I had a card - I was thinking "external" - but apparently an internal USB PCI card is the equivalent.
Well, finally I tried plugging directly into the motherboard USB port and it worked! Always something new to learn!