Win16 app not enumerating a directory contents

Re-reading you post, you say:

If the .pcb filename is manually typed in, it gets opened fine.

Is that from within the program that is not listing the files? Because that would rule out file permissions.

The dialog box you are seeing is an ancient version of this:
Link

which has this parameter:
Link

which contains a field called lpstrFilter which controls which file types are listed by the dialog box.

Is there perhaps a ‘.ini’ file which lists the file types the program can see (i.e. sets that field)?
Could those files be different on the two machines?
That would explain the behaviour.

Our posts crossed – I should type faster :-)

Suggest comparing the version and date stamps between machines of the following low level Win API link libraries: COMCTL.DLL, KERNAL.DLL, MSVCRT*.DLL
where ?? denotes 16 or 32 in windows\system or windows\system32 respectively

The file dialog is reminiscent of Borland’s alternative to Microsoft of the era, so would also check for differing versions of Borland OWL(object window library) and Microsoft MFC (foundation classes)(MFC*.DLL)

Basically certain versions of above will coexist but not talk to each other. Some nerdy match making may be required