Jeana,
Go to macro editor in Excel, Mark replace and press F1 the help for Replace will appear, check how the parameters are positioned in that function and position it the same way in VFP. Do not use named parameters, VFP could not understand them.

** Here what Excel Help said about replace
expression.Replace(What, Replacement, LookAt, SearchOrder, MatchCase, MatchByte, SearchFormat, ReplaceFormat)
** so you must do something like:

#define xlByRows 1
#define xlPart   2

oExcel.Cells.Replace([$null], [0], xlPart, xlByRows, .f., , .f., .f.)

Something like this, but not tested