Network Attached Storage Devices

Not sure I follow the question. I am only aware of "shared USB drives" setup on Airport Extreme. These are NAS connected to a switch which is connected to the router. Not USB. I suspect that it would be odd to have something to do with the Airport Extreme setup only because the other iMac DOES see these devices on the same Network. If I had to guess I think there is something configured or broken (software wise) on the iMac that cannot see the NAS. But I have no idea what?

Thanks for the help.
As I mentioned in the first post, there is no firewall on the iMac in question or on the system in general.
Not sure I understand the part about making sure "the affected Mac is set to mount drives on the desktop" I don't have that on the other Mac which does see the NAS in the finder. Yes I can use key + K to connect to the drives using the IP address.

Thanks for your reply. Yes Parallels is up to date latest version with all updates. Have tried with and without it loaded as well.

I can connect via SMB using "connect to server". What I don't know is why it doesn't show in Finder on just 1 of 2 computers.

I was kind of hoping trying a new user profile would do it but alas no such luck. I also changed the name of the NAS and that also doesn't work. I agree there has to be something blocking the awareness in Finder of the NAS on the iMac but I can't figure out what. Whatever it is it does not block using "Connect to Server" though which still works and I can PING the IP address of the NAS devices just fine.

I am stumped on this one. From what I can find or read Airport Extreme does not support uPNP. Is it somewhere I'm not looking?

Ok I figured it out. I had previously designated several devices on my network with specific IP addresses (printers and the NAS devices). They were not being handled by DHCP. The problem is that I had set the router to have a range for DHCP of 192.168.100.100 to 192.168.100.200 but I used IP addresses in that range for the non DHCP devices in the range. Then sometimes when the router was rebooted it would assign a DHCP IP address that I had already set to a printer or the NAS to a computer or WAP device. That is why sometimes I could not see the NAS and other times I could. I have now reset those devices with assigned IP devices to IP addresses outside the range and rebooted the router. Now all my computers see the NAS devices. Pretty dumb error.