Cannot create new message, reply or forward in Windows Live Mail 2011

This happened suddenly today. I have WLM 2011 (Build 15.4.3555.0308) on Vista (with IE9).

There have been no Windows Updates since it was working OK.

I am receiving emails but creating, replying or forwarding will not work.

The top of page headers appear and I can enter Address and Subject but cannot enter into the message area.

Getting message 'Error HRESULT E_FAIL has been returned from a call to a COM component'.

I have repaired all Live Essentials programs via Control Panel but that had no effect.

Help !!

Is it feasible to backup and reinstall?

Thank you.