Hi Judder - Win32 basically means Win95 or later. In between old MS-DOS and Windows 95/98/NT/ME.... there was Windows 3.x, which was a 16-bit operating system - know as Win16.
More specifically, the Win32 API (Application Programmers Interface) is a set of library routines that Microsoft gaurantees to always be present in their Win32 operating system. This means that programmers do not need to worry if the program will run on Win9x, WinNT or WinXP since they all have that Win32 API.
That you get such an error message means that you somehow tries to run a Windows program in DOSBox 😀 Not good.
Please write exactly what you do when this error pops up.
Edit: Go read this words of wizdom first:
Discworld does not load
Discworld I & II Problem in ENG and GER
DOSBox 60 seconds guide | How to ask questions
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