AutoCAD Inventor :: Replace File And Modify Occurrence Name

I need to rename and replace occurences in an assembly, then modify the occurence name.I rename and replace only Farme generator components, which is tested by <condiftion>.What I want to do :

- Num = ABC
- Original filename = toto.ipt
- New filename = ABC_toto.ipt, and Occurence name = ABC_toto

The code :

fileDir contain the file path
docFName contain the original file name (for example, toto.ipt)
Num contain the prefix to add to the name and the occurence name (for example, ABC)
If <condition>Then

                            New_name = fileDir & Num & "_" & docFName
                            Call oFileNameOcc.SaveAs(New_name, True)
                            Call oOccurrence.Replace(New_name, False)
                            oOccurrence.name = Num & "_" & oOccurrence.name
End If

The problem is, the first time I use the macro, the prefix is added twice in the occurence name (the filename is ok) : I obtain ABC_ABC_toto. This happen only the first time, and only on an orrignal Frame Generator assembly.

If I use the macro again, with for example Num = 123, the result is : 123_ABC_ABC_toto.Where is the problem ?