Request.ClientCertificate Collection Type Mismatch

I have used simple asp pages to enumerate value/properties of the
Request.ClientCertificate collection like so:

For Each strKey in Request.ClientCertificate
Response.Write strkey & " = " & Request.ClientCertificate(strkey) & "<BR>"
Next

exactly as suggested in the MSDN documentation here (under the Sample Code
for VBS):
http://msdn.microsoft.com/library/d...921d64e549f.asp

That worked in W2k Pro sp2 ... last year, but I recently upgraded to XP Pro sp2
and now, that simple asp enumeration throws a VBS mismatch error:

Error Type:
Microsoft VBScript runtime (0x800A000D)
Type mismatch
/cryptoasp/clientcert00.asp, line 10

I need to explicitly convert to a string to avoid the error using:
CStr(Request.ClientCertificate(strkey))

When did this change occur??

Note that this explicit casting to a string using CStr is not required for collections
such as Request.ServerVariables