Crystal Report 7 Pro with VB 6.0 SP5

I'm trying to build a report in VB6 using CR7, for this specific report I try to have 3 parameters; for example, Items shipped by ProdutcShipper between 2 dates. I have this formula but it displays a syntax error which I can't find.
.SelectionFormula = "{References.Cname}= '" & frmReports.dbcMedium.Text & "'" & " AND {References.rDate}>= " & DTPicker1.Value & " AND {References.rDate}<= " & DTPicker2.Value & ""
Basically I'm asking to retrieve all Entries to a warehouse by a shipper between some date range.
when I run this, it displays :
Run Time error: 20515
Error in Formula: --- the formula above
It displays the name of the shipper and both dates correctly ---
A Date is required here.
What would be my error?
I really appreciate your help.
Thank you.