Read-Only Problem

Hi,
I have 2 spreadsheets uploaded and share them with a group. I want the group to be able to modify these spreadsheets so have shared the docs with the 'collaborator' box ticked. However, one of the documents is read-only to the group, and no matter how many times I delete it and reload it, it remains thus. Any suggestions?

PS.
Whilst trying to resolve this problem by unsharing/resharing, deleting/uploading, I bombarded my group's inboxes with notification emails. Any way of turning these off?

Thanks for any help,