Hello mf_galberico:
In the case of Server 5.1, the command to invoke was:
run.exe dfconv
Whereas under Server 2.3.1, the command to invoke is:
dfconv.exe
A person could invoke these commands while positioned in any folder or directory, since run.exe or dfconv.exe would be found on PATH, when using a command prompt with environment variables including PATH set for MF COBOL.
The example dfconv command lines in this case specify absolute paths for the three files flsetl.PRO, flsetl.SRT, and flsetl-CRE.dat. This means you could theoretically invoke these dfconv commands while you were positioned in any arbitrary folder or directory.
In the case of Server 5.1, what was your current directory at the time you invoked the command?
In the case of Server 2.3.1, what was your current directory at the time you invoked the command?
Do you see different behavior depending on your current directory?