Every technician gets a permission issue error when trying to raise a new case or save existing ones. I have checked the permission level of each technician over the Ongoing Cases folder, and everything is fine. Why is it happening?
When this error about permission on the Ongoing Cases folder is experienced by all technicians, usually the fault is not at the permission settings, rather the issue might be related to exceeding the space quota of the Ongoing Cases folder. If Team Helpdesk folders (i.e., Ongoing Cases, Resolved Cases, KB etc) are located in a shared mailbox, it is likely that the mailbox space has run out. If the Team Helpdesk folders are located under Public Folders, please check if the particular space quota of the Ongoing Cases folder (or other Team Helpdesk folder) have not exceeded the defined limit that is set by your Exchange admin or policy.
Once you get it rectified (either by removing some of the older case items to free space, or extend the limit), Team Helpdesk should be able to raise new cases and save existing ones.