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As described in Permissions: Users, Groups & Records a record is linked with a number of several groups. Each link, called a permission, describes which of the following 3 rights it has
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When saving a record, at least one group with write rights needs to be present on the record (Zone and System groups excluded).
Troubleshooting
Upload fails
This can happen when the system uses the default permissions (based on the user’s groups). Possible fixes are:
Enabling permission inheritance on the record-type(s)
Making sure that users that are allowed to create/edit/upload are part of at least one group with (default) write rights