I think it probally started with 'finger trouble'.

When starting a new document in Word it opens OK with the default A4 page
settings but when trying to change margins or page size a message appears,
see attachment. Interesting it allows changes from A4 to letter/legal but
then not allow it to be changed back to A4. ow can I reset the original
default settings, I have tried repalcing the existing with a known good
Normal.dot but this picks upt the same problem.

Any help would be greatly appreciated.