Adding a variable string comment to a cell. "Object Variable or WIth Block Variable Not.."

[NicholasL]

So this is the relevant portion of code.
The error comes up with the last line where I add the comment.

Range("B1").Select
mystring = ActiveCell.Value
ActiveCell.Offset(0, 1).Select

Do
If IsEmpty(ActiveCell) = False Then

    mystring = mystring & ", " & ActiveCell.Value
Else
End If
ActiveCell.Offset(0, 1).Select
Loop Until IsEmpty(ActiveCell)


Worksheets("Results").Activate

TickersResults.AddComment (mystring)


End Sub

I just tested the string with this line

Range("A30").Value = "" & mystring & ""

and the cell turns the appropriate value, so the string functions perfectly.
Not sure what the error is with adding the comment.
Any ideas?

Thanks a lot in advance