From Microsoft: You must make a registry entry to be able to use a UNC path as the current directory.
WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.
Under the registry path:
add the value DisableUNCCheck REG_DWORD and set the value to 0 x 1 (Hex).