Your computer's use of a ; as the regional list separator is fouling you up. VBA is very EN-US-centric so the Range.Formula and Range.FormulaR1C1 expect a comma (,) as the function's argument list separator.
Range("BC" & ActiveCell.Row).Formula = "=IF($BB" & ActiveCell.Row & "=" & """" & "REVIEW" & """" & ", IF(ROW($BB" & ActiveCell.Row & ")<MAX(IF($BB:$BB=" & """" & "OK" & """" & ", $A:$A)), IF(TODAY()-$AY" & ActiveCell.Row & ">=3, " & """" & "DROP" & """" & ", " & """" & "REVIEW" & """" & "), " & """" & "REVIEW" & """" & "), " & """" & """" & ")"
Alternately, Range.FormulaLocal property or Range.FormulaR1C1Local property can be used with your own semi-colon as the list separator.
Range("BC" & ActiveCell.Row).FormulaLocal = "=IF($BB" & ActiveCell.Row & "=" & """" & "REVIEW" & """" & ";IF(ROW($BB" & ActiveCell.Row & ")<MAX(IF($BB:$BB=" & """" & "OK" & """" & ";$A:$A));IF(TODAY()-$AY" & ActiveCell.Row & ">=3;" & """" & "DROP" & """" & ";" & """" & "REVIEW" & """" & ");" & """" & "REVIEW" & """" & ");" & """" & """" & ")"
Your doubling up double quotes within a quoted string is a bit verbose and xlR1C1 notation would save some steps. TEXT(,) is the same as "" in a formula; each produces the same zero-length string.
Range("BC" & ActiveCell.Row).Formula = "=IF($BB" & ActiveCell.Row & "=""REVIEW"", IF(ROW($BB" & ActiveCell.Row & ")<MAX(IF($BB:$BB=""OK"", $A:$A)), IF(TODAY()-$AY" & ActiveCell.Row & ">=3, ""DROP"", ""REVIEW""), ""REVIEW""), TEXT(,))"
'.FormulaR1C1
Range("BC" & ActiveCell.Row).FormulaR1C1 = "=IF(RC54=""REVIEW"", IF(ROW(R:R)<MAX(IF(C54:C54=""OK"", C1:C1)), IF(TODAY()-RC51>=3, ""DROP"", ""REVIEW""), ""REVIEW""), TEXT(,))"
The xlA1 and xlR1C1 formula rewrites above each produce the following when ActiveCell is on the second row.
=IF($BB2="REVIEW", IF(ROW($BB2)<MAX(IF($BB:$BB="OK", $A:$A)), IF(TODAY()-$AY2>=3, "DROP", "REVIEW"), "REVIEW"), TEXT(,))
As I mentioned in comments above, that formula would seem to be an array formula. In that case, use the .Formula comma based rewrite but change the Range.Formula property to Range.FormulaArray.
Debug.Printthe string, grab it from the immediate pane (Ctrl+G), paste it into an empty cell. Excel will tell you what's wrong with it, if it doesn't jump at you right away from the debug output.=IF($BB2="REVIEW";IF(ROW($BB2)<MAX(IF($BB:$BB="OK";$A:$A));IF(TODAY()-$AY2>=3;"DROP";"REVIEW");"REVIEW");"");to,or use .FormulaLocal instead of .Formula.MAX(IF($BB:$BB="OK";$A:$A))part tells me that should be .FormulaArray, not .Formula.