Ok, i have cracke it, i pasted this function code into the VB editor for my workbook. It now highlights correctly and should not display any name error!
Sub comments()
End Sub
Function CommentText(Cell As Range, Txt As String) As Boolean
Dim x As Comment
Set x = Cell.Comment
If x Is Nothing Then
CommentText = False
Else
CommentText = x.Text Like "*" & Txt & "*"
End If
End Function