Bt Inspiration - Voicemail Module - Help!

I have just purchased and installed the Voicemail module for my BT Inspiration system. I'm not a telecomm engineer by any sorts but simply powered down system, plugged it into slot 18 as instructed and powered back up.

The featurephone now has various voicemail options showing on the menus which I assume means the module has been installed ok? Anyway, the only reason I have got this module is for recording personalised Courtesy Greetings but when I select "Record Greeting" it comes up "Voice Box Full" and doesn't allow me to record anything even though this is the first thing I have attempted to do.

I have tried "Replay Greeting" and this has nothing but silence and have also tried "Delete Greeting" but this option doesn't do anything.

I'm kind of stuck and don't know what to do next. There doesn't appear to be an Empty or Reset Voice Box option anywhere. If you can help this would be great otherwise should I assume the module is faulty???

Thanks

Steve