Macro canīt be fired from another worksheet

Hello,

I've got the following macro in my workbook, and it works correct if started from the macro dialog box.
Iīve assigned the macro to a button on another worksheet, but it fails to fire the macro.

Am I right in assuming the macro needs editing (worksheet defining) in order to be fired from another worksheet?
I haven't found any reference to this problem on the net.

Sub Stack()
Dim iRow, iCol, iTargetRow, iMaxRow As Long
iMaxRow = 10000
iTargetRow = 4
Columns(55).Clear
For iCol = 39 To 43
For iRow = 4 To iMaxRow
If Cells(iRow, iCol) > "" Then
Cells(iTargetRow, 55) = Cells(iRow, iCol)
iTargetRow = iTargetRow + 1
Else: Exit For
End If
Next
Next
End Sub

'Change iMaxrow = 500 to the actual maximum row for your data.

'Uncomment the If and End If lines to prevent blank cells from being included in the stack.
'Uncomment the Else line also to skip to the next column when the first blank cell in the current column is encountered.
'Uncommenting all three lines would allow you to use a very high iMaxRow value without extending the macro run time but could lose data if there could be any "internal" blank cells.

Vincent