Document has SAP objects assigned

What causes this issue?

You have entered the deletion indicator for the document, so the
document is to be deleted during the next reorganization run.
As this document has objects linked to it, you see a warning message.

How to fix this error?

Check again whether you really want to delete this document.
To continue processing, confirm this warning message. Once you have set
the deletion indicator, you can only use display functions or change
the deletion indicator.

Error message extract from SAP system. Copyright SAP SE.