What is the location of the program (within your Windows filesystem) and how did you try to mount and access it? Posting the exact commands you used will help.

on a more general note, be advised that database apps are a bit outside the scope of DOSBox and there are no guarantees that they would run reliably.

What directory and how did you create it?

I suspect you mean the directory you mounted as C, since you didn't provide more information, I'll go with that.
Well, *IN* Dosbox that directory is the root of C:\. You can't change directory to it since you are already there when you change to C:\

For. Example, if you made the folder DOS on your REAL harddrive C:\ and then use the commands in Dosbox
mount c C:\dos
C:

you ARE in reality in C:\dos but for Dosbox that folder is now C:\
I hope I didn't confuse you now 😉

Thanks guys,
I hadn't realised after typing "mount c:\rpd" I was already in the new directory when I was at the C: prompt, so I typed in the comand rf.com and my rapidfile program runs!!

Thanks again