DOS exe not working in DOSEMU under Ubuntu 16.04

I've been using DOSEMU under various versions of Ubuntu for many years, 
and still rely on it.

I've just installed a new Lubuntu 16.04 64-bit system, and installed 
DOSEMU on that, using the same DOSEMU and Freedos configurations as on 
the previous Lubuntu 14.04 system.

Everything seems fine, except for one very old DOS exe which has worked 
fine for over 15 years, but now doesn't.  It simply exits immediately 
and silently with no error messages.

As far as I can see, the only difference from the working system is the 
change from Lubuntu 14.04 to 16.04.

Any suggestions on how to set about discovering what's wrong?

Many thanks in advance!

Gordon
+44 (0)7732 696122