Hi,

I think XL2010 is a bit fussier about referencing objects.
Which debug line is highlighted?

If the IF...line then
IF SheetCodeName.Range("Check") = "Duplicate" Then

If the .Copy line then
SheetCodeName.Range("L12").Copy

Note SheetCodeName is the VBE Sheet Code names not the tab name. Always use SheetCode names wherever possible in case a user changes a tab name.

If this doesn't fix the problem upload the workbook