But does the network show in the tree panel at all? If not, see Options | Preferences | Disks & Folders | Turn off "Do not show network branch".
If the network does show, but not any shared drives or devices within it, go to the same dialog and try tagging the option "Public Locations" in the lower right corner.
If that still doesn't help, could it be that you're running ThumbsPlus from an account that has no access to those locations?
As a work around, have you tried to map those locations to drive letters?