I've checked all the file names etc in the test run and they are all ok which I thought they would be as they have all been generated from the same excel document so if it was down to a counter not updating (sorry I have no idea what this means ) is it possible that it could be a frequent problem? I wouldn't know until all the emails had sent (it took a while to do 17 never mind 400!) so wouldn't want to have to do that more than once, and I don't suppose our clients will want to receive multiple emails each month or is there something I can check to make sure they are updated before sending?

Thanks again for all your help, its much appreciated!