​​The User or Group Id 'X' Could Not Be Resolved - User/Group Cannot be Found (SharePoint)

Error Example:

The user id <ID> could not be resolved on the target system at 'https://<SPSite>/<subSite>/<List>/': User cannot be found.

The user or group id <ID> could not be resolved on the target system at 'https://<SPSite>/<subSite>/<List>/'​: Group cannot be found

 

Cause:

This guide applies to both versions of this error for User ID or Group ID.

This occurs when a user or group is being added to a Person/Group fields does not exist in the User Information List for SharePoint. This may be because the user/group has since been removed from SharePoint/Active Directory is still assigned to a file as the creator (Author) or Modifier. It could also be the user was never given access or has never logged onto the site before. 

Resolution/Workaround:

This error is more of an annoyance than an actual issue​ and can be safely ignored. If you do wish to clean them, you will need to find and update the files that contain the removed user so that they are no longer the listed in Person/Group field.

If this is not obvious, you can use the following Odata query to identify which objects in the Library still have the user ID assigned. In the example below, it is assumed that it is the Author field (Created By) or Editor (Modified By) that has the invalid username, but you could use any Person/Group field in this query:

https://<RootSPSite>/<subSite>/_api/lists/getbytitle('<ListName>')/items?$select=Id,Author/ID,Author/Name,Editor/ID,Editor/Name&$expand=Author/ID,Author/Name,Editor/ID,Editor/Name&$filter=(Author/ID eq <ID> or Editor/ID eq <ID>​)

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This should output all records that have that User ID, with the ID field itself marking which internal SharePoint ID the document is.

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