Outlook Web Access – TEXTAREA does not display

I have encountered a problem on my pc, where when logging onto OWA, everything works fine, but as soon as I open a reply or new message window, the TEXTAREA is displayed with a red X.

I am astouned, as nothing has been installed or removed! It worked perfectly until recently…

Any ideas how to fix this?
I am in need of fast help as I cannot reply to anyone already for a week!