Thanks for the replies Tracey/Craig - I thought I would try the latest
patch
for Bordermanager - Field Patch 3F that came on on December 17th as
this
included an updated alcheck.nlm along with a number of other files, to
see
if this resolved any corruption and it has seemed to work. I
re-enabled the
Enforce Access Rules and there was no problem with timestamp
synchronisation
and no 403 errors for users.
Cheers Martin.