ICAL Delegate calendars no longer appearing

Currently, we run an internal network of 9 computers. We share calendars using iCal server. We do not permit access to the server other than via hard wire. Each staff member has their own iCal account, visible to everyone else. We have had an ongoing issue with the iCal server arbitrarily not recognizing individual passwords, which I solved by going into iCal server and resetting the passwords. Access would then be restored. This morning, the same error message began popping up on everyone's ical. When I reset the passwords, instead of access being restored, we now get the error message that access to the other calendars is "forbidden." However, it is not the same on each computer, some have access to no other accounts, some have access to 2 or 3, no one has access to all.

I tried deleting my own account and then re-creating it, but it is still not visible on other computers. Any ideas on how I can get this system up and working again?