Have you added any toolbar buttons:
I would first try restarting Acrobat to see if that fixes the problem.
If not, then under "Help" use the "Repair" opton.
Thanks for the reply.
I haven't added any toolbar buttons and I've re-started Acrobat / computer several times.
As I mentioned in my original post, I've tried a repair but that didn't work either.
Don't worry. I have fixed it by completely removing the software and re-installing it.