I have an MVP410 with ver 6.06 calling an MVP410 ver 6.05: calls complete OK but I cannot send DTMF. Both ends are out of band fixed duration, Is there a cure?

This is a known issue when using an X.05 version with X.06. If you upgrade the 6.05 to 6.06 or downgrade the 6.06 to 6.05 then the DTMF will work. This will be fixed in an upcoming version.