An ITRS OP5 Monitor user that is in the group limited_edit, that is created on a default installation cannot edit hosts and services for which the user is a contact. This issue manifests itself by after pressing the submit button in an edit form of a host or service, a blank page is shown and there is a
NacomaRelationException error in
It happens if a user that has permission to edit an object tries to do so without having permission to view the host/service template that the object uses.
As an administrator, go to Manage / Configure / Group rights and for the group having the issue, enable permissions "Host Template View All" and "Service Template View All":