Deserialize dictionary with datacontractserializer c#

Question

I want to deserialize a dictionary with datacontractserializer, the xml schema is the following :

<General xmlns="http://schemas.datacontract.org/2004/07/MyProject" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<Mydictionary xmlns:a="http://schemas.microsoft.com/2003/10/Serialization/Arrays">
    <a:KeyValueOfunsignedByteMyclass>
        <a:Key>1</a:Key>
        <a:Value>
                     ....
        </a:Value>
    </a:KeyValueOfunsignedByteMyclass>
    <a:KeyValueOfunsignedByteMyclass>
        <a:Key>2</a:Key>
        <a:Value>
                    ....
        </a:Value>
    </a:KeyValueOfunsignedByteMyclass>
</Mydictionary>

But on deserializing, I get this error :

"An item with the same key has already been added."

(referencing KeyValueOfunsignedByteMyclass)

Can someone help me to resolve this problem please?

Thanks