Deserialize dictionary with datacontractserializer c#

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

1 .... 2 ....
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