ACER Monitor won't work with a BUSH Set Top Box

I have an ACER model P221W LCD Monitor and a Bush DFTA10HD Set Top Box.

I use the ACER monitor with my computer via the VGA connection and I would also like to occasionally use it to display a TV picture from

the Bush Set Top Box.

The Set Top works with a CHEMEI LCD Monitor via the VGA connection but it will not work with the ACER monitor.

It also works with my TV via the VGA connection.

When I connect it to the ACER monitor via the VGA connection, the screen shows a message "Input signal not recognised" or words to that

effect.

The Bush also has a HDMI output and the ACER has a DVI input, so I connected them via a DVI cable & HDMI converter. But the same message

appeared on the screen.

Does anyone know why? I assume it is due to incompatible DDC data.

Any assistance will be appreciated.