CheckSignature fails on ds:SignedInfo

Hi!
I try in net 2.0 and c# visual studio 2005 to verify signature stored
in SignedInfo with 'ds:' prefix (signature was generated in other
application).
Part of signed xml document:
....
<ds:SignedInfo>
<ds:CanonicalizationMethod
Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#WithComments";></ds:CanonicalizationMethod>
<ds:SignatureMethod
Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1";>
</ds:SignatureMethod>
<ds:Reference Id="idDoc1" URI="document.doc">
<ds:DigestMethod
Algorithm="http://www.w3.org/2000/09/xmldsig#sha1";></ds:DigestMethod>
<ds:DigestValue>WPRjvseeq1HUf/d6KR7JMxx/I/A=</ds:DigestValue>
</ds:Reference>
</ds:SignedInfo>
....
CheckSignature always return false... but signaure is sure valid!
I was try to get description of reason of failed verification - but
dont know how get this.
I think, reason is ds: prefixes in SignedInfo?
So, is posible verify this signature correctly with CheckSignature - to
get status true - valid, when SignedINfo has ds: prefixes?
Please for help!

.

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