Converting Access string to DBTYPE_DATE

I'm using Access 2010 and have a routine that sends parameters to an Oracle procedure.
It works great for strings (adChar) and Numbers(adDouble) but I'm trying to send it a date.
I think it needs a DBTYPE_DATE.

I dim:
Dim cPW As New ADODB.Command
Dim aPNames() As ADODB.Parameter

Then I set the "core":
Set aPNames(iCount) = cPW.CreateParameter(, adDBDate, adParamInput)

Then I get to the point where I assign the value
  cPW.Parameters.Append aPNames(iCount)
  aPNames(iCount).Value = aParam(iCount, 3)

aParam is a string array. Aparam(iCount,3) is "20110501".

I get the error:
Application uses a value of the wrong type for the operation


What do I need to send it  and how do I get there?