Can't access mapped drive

I have three mapped drives that I can't access by drive letter, but I can access them via the Network. The drive icons have a red X displayed. For example, I get a "Location is not available" window with the contents: "N:\ is not accessible. The device is not ready." If I expand the Network in File Explorer, I can access the folder from there. I can also access them as mapped drives on my other computers. I thought about trying to unmap them and remapping again, but I haven't figured out how to do that. Two of the drives are in a D-Link NAS and the third is a 10 TB RAID in another Win 8 computer. Any Suggestions?

 

I tried the disconnect option and it appeared not to do anything. Later today I did a reboot and the drive letters were no longer present. I mapped the drives again and all is well.

 

What happens when you disconnect and reconnect it?

Commands:

net use x: /delete
net use x: \\servername\shared folder\public\

(replace the X: with your drive letter)