On MediaCheck, an error popup occurs showing:

No such entry
Data: mmf

The solution for the problem is to add the lines

&mmf: mm\mmf.exe,mm
&muf: mm\muf.exe,mm

to the backup server Hiback\CONDEV file.

Restart the backup server service NBK DC Remote Command Executor to make the CONDEV changes effective.

Repeat the MediaCheck.