Spell Checker - no dialogue box appears

Hello all,

I've got this occasional problem using the following:
MS Word - 2003 version
XP Prof SP 2
Occasionally when using spell checker an error occurs when using it. I press
the icon and a word is highlighted as it is spelt wrong, but no dialogue box
appears to make a spelling suggestion.
If the document is closed and restarted it works fine.

Has anyone come across this before?

Thanks for any hints and tips.

Cheers


Greg