After doing nothing special (just a few append and delete queries) about 1/3 of linked tables became corrupted in some of their fields (#error). I restarted the pc and did a compact and repair which did not work. I deleted and re-established the links which fixed the problem.
Has anyone any idea why this might have happened? Is this a "feature" of Access 2010 that I have to live with, or was I just unlucky?