Delete Rows Not Matching Date Variable

I have a need to call a sheet from another sheet, copy two pages from the newly opened, existing sheet to a new workbook, search one sheet of the new workbook for any entries that don't contain a variable I specify, which is the first four digits of the field, and delete them. The sheets represent a daily view of jobs (identified by the "RptDate" variable) and an entire monthly list of jobs, which I want to delete all of them not from the date specified in the variable "RptDate". The fields in column A contain the date in "mmdd" format as the first four digits, and I have that specified in the "B1" celll of the originating workbook.

I found some code in this link Search Column Delete Row If Value Found that looked good. I had to modify it since I needed to search for a variable (RptDate) and needed to search column A and start on row 8 of that column. My current code looks like this:

Sub Macro1()

Dim RptDate As String
Dim RptMonth As String
Dim iLastRow As Long
Dim i As Long
RptDate = Range("B1").Text
RptMonth = Range("B2").Text
Workbooks.Open Filename:=(RptMonth)
Sheets( Array(RptDate, "Total Database")).Copy
iLastRow = Cells(Rows.Count, "A").End(xlUp).Row
For i = iLastRow To 8 Step -1
If Left(Cells(i, "A").Value, 4) <> RptDate Then
Rows(i).Delete
End If
Next i
End Sub

It works fine right up to the "Rows(i).Delete" line. It errors out with a "run-time error 1004, delete method of range class failed" and highlights the above line. I know the fields I'm pulling the variables from are working right since it opens the correct workbook off of one of them.