Just in case they are Chr(10) perhaps this would be better.
ActiveSheet.Cells(i, x).AddComment _
application.TRIM(replace(replace(olTsk.Body,chr(13 )," "),chr(10)," "))

But you definitely don't want to use CLEAN which will remove
characters and not put a space in it's place. More on CLEAN in
http://www.mvps.org/dmcritchie/excel/join.htm#trimall
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HTH,
David McRitchie, Microsoft MVP - Excel [site changed Nov. 2001]
My Excel Pages: http://www.mvps.org/dmcritchie/excel/excel.htm
Search Page: http://www.mvps.org/dmcritchie/excel/search.htm