Run time error in my macro

I have this code which Robb came up with and it works fine, but when i make a modification, i get an error.

This is the working code:

Sub Directory_Search()

Dim myFile As String, myCurrFile As String
myCurrFile = ThisWorkbook.Name
myFile = Dir("S:\FileServer\Excel\Save FILES In Here\YEAR 2001\01-01\Cathy\*.xls")
Do Until myFile = ""
Workbooks.Open "S:\FileServer\Excel\Save FILES In Here\YEAR 2001\01-01\Cathy\" & myFile

Workbooks(myCurrFile).Worksheets("Sheet1").Range("A65536").End(xlUp).Offset(1, 0) = Workbooks(myFile).Worksheets("Application").Range("AI4")

Workbooks(myFile).Close savechanges:=False
myFile = Dir
Loop

End Sub

But it WILL NOT work like this:

Sub Directory_Search()

Dim myFile As String, myCurrFile As String
myCurrFile = ThisWorkbook.Name
myFile = Dir("S:\FileServer\Excel\Save FILES In Here\YEAR 2001\01-01\Cathy\*.xls")
Do Until myFile = ""
Workbooks.Open "S:\FileServer\Excel\Save FILES In Here\YEAR 2001\01-01\Cathy\" & myFile

Workbooks(myCurrFile).Worksheets("Sheet1").Range("A65536").End(xlUp).Activate
With ActiveCell
.Offset(1, 0) = Workbooks(myFile).Worksheets("Application").Range("AI4")
End With

Workbooks(myFile).Close savechanges:=False
myFile = Dir
Loop

End Sub

Notice I changed:

Workbooks(myCurrFile).Worksheets("Sheet1").Range("A65536").End(xlUp).Offset(1, 0) = Workbooks(myFile).Worksheets("Application").Range("AI4")

to:

Workbooks(myCurrFile).Worksheets("Sheet1").Range("A65536").End(xlUp).Activate
With ActiveCell
.Offset(1, 0) = Workbooks(myFile).Worksheets("Application").Range("AI4")
End With
I'm getting the error "Run time error '1004': Activate method of Range class failed. " with the bold part

I know its not much different, but for the sake of knowing, I'd like to know :)

Can someone help? Thanks :)