When you reference Range like that it's called an unqualified reference because you don't specifically say which sheet the range is on. Unqualified references are handled by the "_Global" object that determines which object you're referring to and that depends on where your code is.
If you're in a standard module, unqualified Range will refer to Activesheet. If you're in a sheet's class module, unqualified Range will refer to that sheet.
inputTemplateContent is a variable that contains a reference to a range, probably a named range. If you look at the RefersTo property of that named range, it likely points to a sheet other than the Activesheet at the time the code executes.
The best way to fix this is to avoid unqualified Range references by specifying the sheet. Like
With ThisWorkbook.Worksheets("Template")
.Range(inputTemplateHeader).Value = NO_ENTRY
.Range(inputTemplateContent).Value = NO_ENTRY
End With
Adjust the workbook and worksheet references to fit your particular situation.