dosbox version?

latest, 0.74

Reinstall the app inside dosbox, and post the exact mountings/installation instructions you performed.

I don't have a kit for the app. It works fine under windows xp. The only command given in dosbox is mount C: D:\appfolder then running the app

The only command given in dosbox is mount C: D:\appfolder then running the app

That's most likely the problem.
Since the app wasn't installed from within Dosbox it most likely expects to be at d:\appfolder not in the root of c:\ (where the mounting puts it). You can test two things...
- mount c D:\ (and then "cd appfolder", then run the app), or
- mount d D:\ (and then "cd appfolder", then run the app)

moving the app inside a compatible o/s doesn't affect it. It runs wherever it is. I tried leaving the same virtual file path as the original path inside dosbox and it doesn't help at all. The idea is that the app starts inside dosbox, but as soon as I'm trying to access a file it stops responding. I tried running dosbox with admin privileges and also checked the security permissions of the app's folder.

Ok, are you sure that Dos is a compatible platform then? You could try this by going the boot image way in Dosbox. Put it on a disk image, boot from that and see whether it works in that. If it does then it uses some function that is not implemented in dosbox, if it doesn't then it isn't a pure dos app 😀

i'm pretty sure it's a dos program since I can run it in a virtual machine loaded with dos/win98/or winxp. The only problem with running dos on a virtual machine is that you can't share guest folders and actually use the program. But, yes. I'm sure. I would attach a copy of the application but I doubt you would understand much of it since it's a partially translated french application, translated in romanian :p.

If you use the debug-enabled version of DOSBox, it will tell you the path of the files that the program is trying to access. You might then be able to see how you need to change the mountings.

Also, if your program does math, once you get it to run be sure to use core=dynamic in the configuration file, and a 32-bit x86 version of DOSBox (such as the standard Windows version). Otherwise you might get inexact results.

You might get both inaccurate as well as wrong results with all cores, but well 😉