Could be a number of things. It's possible that when the software was installed, it stored additional information somewhere on the drive as a copy protection mechanism. Did you install the software from its original media in DOSBox, or did you just copy the files from your XP machine? If you did the latter, is the program running in DOSBox from the same directory as it was running on the other computer? That is, if you used to run it from C:\DOS on XP, did you copy it over to C:\FOOBAR\DOS on your Windows 7 computer and then mount C:\FOOBAR as drive C in DOSBox?

Another possibility is that the program is trying to use low-level disk access. To check this, you'll have to boot DOS from a disk image within DOSBox.

In the future you will want to ask DOSBox questions in the DOSBox forum.

Hi Jorhpo,

Thanks for this. Do you have instructions how to boot a disk image within DosBox? Also yes, there is no real installation as such, you just copy the folder, and run the exe, that should do it. In the past sometimes I have to increased the files and buffers in Windowsnt.Config file. Can this be done in a similar config file in DosBox?

@Collector. The forum link on DosBox sent me here 😀

There should be an appropriate topic in the Guides forum. If the program fits on a floppy, then the easiest way to get going is to:
-find an MS-DOS (or FreeDOS or Win98 or whatever) bootdisk image from somewhere
-Put your folder in the disk image using Disk Explorer or Winimage
-Boot the image in DOSBox using the "boot" command

This is pretty much the only way to effectively adjust "files" and "buffers" in DOSBox, but I stress that this is typically not necessary.

If this is a text-based program with no fancy graphics (a Clipper program, perhaps? Those are the ones that usually come with specific Files and Buffers requirements), then you should try it in vDosPlus first.