Thanks :) It's XL2010.

I seem to have got it working, touch wood, through a combination of:

1) Storing the list of filenames in an array, i.e. doing the DIR loop first not during the main code.

2) Putting in application.waits of 1 second where files are being opened, closed or saved, to give Excel and the network drive time to sync

It seems to be working so far.