Most of the time that's a reference to 'mapping a drive' or assigning a drive letter to a network share. In this context it seems odd that a network map has an effect.
There are issues with long directory names in old applications but the usual is to not exceed 8.3 naming conventions. The reason Pro might differ is that some directory is over the 8.3 naming or the 8.3 support was turned off. Think about that. I won't write more about 8.3 since you can use the web to learn about that.
I have used PCFocus 5.5 for years (since approx 1990). It has worked fine in a DOS window under all Windows versions thru XP on many different notebooks and desktops. I recently attempted to get it to run under XP Pro. No go. Focus invokes, but cannot find the data files (I get this same occurrence on all machines I have running XP Pro). I think this may be a mapping issue but I cannot find the help I need to fix it. Any help would be greatly appreciated.