You might want to take a look at these questions/answers ; they could give you some informations concerning your problem :
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javascript access parent DOM across domains?To make things short : accessing iframe from another domain is not possible, for security reasons -- which explains the error message you are getting.
The Same origin policy page on wikipedia brings some informations about that security measure :
In a nutshell, the policy permits scripts running on pages originating from the same site to access each other's methods and properties with no specific restrictions — but prevents access to most methods and properties across pages on different sites.
A strict separation between content provided by unrelated sites must be maintained on client side to prevent the loss of data confidentiality or integrity.