I already asked a question like this before, but seems that the answer given is not working in this case
this is my code:
Worksheets("Sheet").Range(myRange).formula = "=CONCATENATE(CODICI!" & stringCodiceCella & ";" & stringDesignazioneCella & ")"
Note that stringCodiceCella is a String, and stringDesignazioneCella is also a String.
Following this link A working example of formula in VBA
I can't see the error.