Error: INSUFFICIENT_ACCESS_OR_READONLY
The above error generally occurs when a user tries to modify or delete a record that was created by someone else. If an error like the one in the picture occurs on the Inventory Assignment screen, you can fix it by adding the Modify All permission for:
- Inventory Assignment
- Inventory Item
This can be done directly on the profile, or by creating a new permission set. For more information about creating Permission Sets, check here