Sorry I haven't been at a computer for a while

to have seen your response. I'm currently updating to the latest 1.2 and will try this out again. Just a note, I have a huge library (60K ..I know, I know..for those who comment on the size...) and when this happened, I was updating I think it was around 600 entries.
The way I did this originally was use the tag browser and click on the rating (for example 4 stars), then in the list window highlighted all the entries, and used the bulk edit metadata button. I set the rating to 0 and then clicked OK.