Not able to attach files in PM

I get a "Spam" error message whenever i try to attach any files in the PM. Can you please help ? It is the same with any attachment file ... (i tried with xls, ppt, doc, txt, etc)

Below is the exact error message ...
"Invalid Post specified. It is possible that the Post has been deleted for anti-spam control or a duplicate Post (for example). However, if you think you followed a valid link which should not be delete please contact us in the forums and post the invalid link."

Thank you !

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