Ok this is weird

On my works computer I cant seem to reply, delete, forward or move my emails when I am in the message but I can do all of them (well apart from reply and forward) when I just need to tick the box

why??? It has only just started doing this over the last week or so and its really annoying me now

Everytime I have to compose a new message if I want to reply to someone.
Ive checked at home and its fine
Does anyone have any idea why?