I do believe the President has the right to invoke Executive Privilege to withhold documents from Congressional Oversight. But only in limited circumstances. The current attempt by the Obama Administration clearly is outside those limited bounds.
The key bit? From Issa’s letter to the President in response:
In his letter, the Attorney General stated that releasing the documents covered by the subpoena, some of which he offered to the Committee hours earlier, would have “significant, damaging consequences.” It remains unclear how — in a matter of hours — the Attorney General moved from offering those documents in exchange for canceling the contempt vote and ending the congressional investigation to claiming that they are covered by executive privilege and that releasing them — which the Attorney General was prepared to do hours earlier — would now result in “significant, damaging consequences.”