What am I doing wrong here?

I've searched this discussion group, and google groups, but can't find the
solution to the error, or an alternate way to code this. This code sorts the
worksheet by the dates in column B, then searches the cells in the column
looking for the last instance of myDate. (I need the address so I can select
a range and move it to another worksheet.) But I keep getting stuck with this
"Object var... not set" error.

If I'm missing something fundamental here, please point me in the right
direction. I've spent several hours looking for and trying alternate ways of
doing this, and researching setting object variables, but I keep ending up
back at the same error.

Private Sub btnDate_Click()
UserForm1.Hide
Range("A1:E261").Sort Key1:=Range("B1"), Order1:=xlAscending, Header:= _
xlGuess, OrderCustom:=1, MatchCase:=False,
Orientation:=xlTopToBottom, _
DataOption1:=xlSortNormal
If opt8.Value = True Then iDays = 9
If opt15.Value = True Then iDays = 16
If opt31.Value = True Then iDays = 32
'using "Set myDate = Date - iDays" gets error on next line
myDate = Date - iDays
'select column B to search in
Cells(1, 2).Activate
ActiveCell.End(xlDown).Select
strLast = Selection.Address
Set myRange = Range("B1", strLast)
'as written, error occurs on next line
myRange.Find(what:=myDate, lookat:=xlPart).Select
strLast = Selection.Address
Set myRange = Nothing
End Sub

Any help would be extremely appreciated!