Just an update - I think I've got this sorted.
I went into the properties of the OGM and in the 'Key Response' tab I set them all to 'No Response' (Especially the one that had a respose to 'leave message') This seems to have done the trick. There must have been something in the message that IVM was picking up on
Just noticed on the bottom display window - Caller pressed Key [1] - when the message is playing. This is even happening when I change the message. Not going to worry too much about it now
If you have any Ideas about the Caller Id thing - would love to hear them
Regards
Stephen