iTunes Backup locked without setting password !!

Hi
I have iPhone 4 with ios 4.2.1 , after upgrading to ios 5.1 and try to restoring
My data i found that the backup file locked ( encrypted ) by it self !!!
I`m sure i did not set any password while i am doing the backup.
Tried the following password :
0000-1111-1234-12345-Apple ID Password-iPhone password
But not one success

Please can you help me to retune my data such as Notes,Contacts ...etc. ?

 

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Nobody can help ?