protected sheets - VBA error

[habids]

hi, I need help.
When I protect my worksheets VBA error notifications come out.
All cell are Locked.
Thank you vermu much.
error 1004.jpg

VBA:
Sub HideRowCellEmpty()
StartRow = 31
LastRow = 510
iCol = 21
For i = StartRow To LastRow
If Cells(i, iCol).Value <> "" Then
Cells(i, iCol).EntireRow.Hidden = False
Else
Cells(i, iCol).EntireRow.Hidden = True
End If
Next i
End Sub

[habids]

oh I solved with this:

Sub HideRowCellEmpty()
Worksheets("Test1").Unprotect Password:="pass"
StartRow = 31
LastRow = 510
iCol = 21
For i = StartRow To LastRow
If Cells(i, iCol).Value <> "" Then
Cells(i, iCol).EntireRow.Hidden = False
Else
Cells(i, iCol).EntireRow.Hidden = True
End If
Next i
Worksheets("Test1").Protect Password:="pass"
End Sub