Unable to set hidden property of the Range class

Hi

There have been quite a few posts relating to this - but none has solved my problem.

I have some vb that hides rows in a report where it comes across an empty cell:

Sub HideRow(HideRange As Range)
' Hide rows where missing data
    For Each c In HideRange
        If c.Value = "" Then
            c.EntireRow.Hidden = True
        Else
            c.EntireRow.Hidden = False
        End If
    Next c
End Sub

I select a parameter from a dropdown and this updates the report. I then call the vb with Call HideRow(Worksheets("3.3").Range("c9.c68"))

Sometimes I get the message: Runtime error 1004: Unable to set hidden property of the Range class.

Its intermittant and I've been unable to identify a pattern.
There are no comments or objects on the sheet.

Thanks