The issue could be related to this one from the knowledge article here:
Description
This error occurs on a VisualForce page when a related list is being
referenced but isn't available on the user's page. An example of this
error would be
'OpenActivities' is not a valid child relationship name for
entityOpportunity.
The problem can appear confusing when the related list is actually
added to the page layout by the system administrator.
Resolution
However the related list has been removed by the individual user (it
doesn't appear only for the user receiving the error message). The
related list can be added back in by going to:
Setup | My Personal Information | Change My Display | Customize My
Pages | Select the (custom/standard object) from the list | Customize
My Pages.
Add the related list that is referenced at the start of the error
message into the selected list and click save. This should resolve the
error message.
Note: Some child relationship names are not the plural of the object name like the following:
HTML Email Status: "EmailStatuses", Activity History: "ActivityHistories", Notes and Attachments: "NotesAndAttachments", Approval History: "ProcessSteps", Campaign History: "CampaignMembers".