Checkbox that enters username into cell to the right

Hello Everyone, I have a spreadsheet, and on some of the worksheets there are checkboxes in in the O column. When checked the VBA code I have should automatically put the persons username in the P column of the same row in which the box was checked.

This worked excellent when I had only one worksheet. Now that I have multiple sheets I am getting an error message.

The code is:

[code]

Sub Process_CheckBox()

Dim cBox As CheckBox

Dim LRow As Integer

Dim LRange As String

LName = Application.Caller

Set cBox = ActiveSheet.CheckBoxes(LName)

'Find row that checkbox resides in

LRow = cBox.TopLeftCell.Row

LRange = "P" & CStr(LRow)

'Change date in column B, if checkbox is checked

If cBox.Value > 0 Then

ActiveSheet.Range(LRange).Value = Environ("USERNAME")

'Clear date in column B, if checkbox is unchecked

Else

ActiveSheet.Range(LRange).Value = Null

End If

End Sub

[/code]

and the error message I get is :

Run-time error '1004':

Application-defined or object-defined error

The Debugger highlights this line in the code:

ActiveSheet.Range(LRange).Value=Null

The workbook can be viewed here....

https://onedrive.live.com/redir?resid=1133973B98CD486!340&authkey=!AHIS2AnLOd7QF7w&ithint=file%2cxlsm

Help?!?!