Actually this does sound familiar. When I used to have my pc set to use L: as a mapped network drive (setup the mapping through Windows Explorer), I would often have to open Windows Explorer and 'open' that drive before C3D would recognize it as available. I don't recall having this issue since I changed how I map the drive....which is via a .BAT file with this line in it:
net Use L: "\\Imaging\D\Land Projects 3" /YES
The YES telling it that it is to be persistent. I only need to run this when the drive letter has been reassigned (on my laptop I also have a .BAT to change the L: to be a local drive for working at home).