Run-time Error '3075'

I have created a form which takes a user-prompted date range and outputs a list of appointments for that date. For some reason when I enter the start date of 11/21/1900 and an end date of 11/21/2000 I am getting the following error:

"Run-time error '3075':
Syntax error (missing operator) in query expression '(HBC
1 Month Between #11/21/1900# And #11/21/2000#)'"

The code is seen below. Could anybody shed any light on this? Thanks.

Private Sub Command4_Click()
Dim strReport As String 'Name of report to open.
Dim strField As String 'Name of your date field.
Dim strWhere As String 'Where condition for OpenReport.
Const conDateFormat = "#mm/dd/yyyy#"

strReport = "HBC 1 Month Visits"
strField = "HBC 1 Month"

If IsNull(Me.txtStartDate) Then
If Not IsNull(Me.txtEndDate) Then 'End date, but no start.
strWhere = strField & " <= " & Format(Me.txtEndDate, conDateFormat)
End If
Else
If IsNull(Me.txtEndDate) Then 'Start date, but no End.
strWhere = strField & " >= " & Format(Me.txtStartDate, conDateFormat)
Else 'Both start and end dates.
strWhere = strField & " Between " & Format(Me.txtStartDate, conDateFormat) _
& " And " & Format(Me.txtEndDate, conDateFormat)
End If
End If

' Debug.Print strWhere 'For debugging purposes only.
DoCmd.OpenReport strReport, acViewPreview, , strWhere
End Sub