I got this lead from Retraction Watch awhile ago:
But it now appears that the Academia.edu takedowns were part of a broader effort to take down unauthorized copies of articles published in Elsevier journals from across the Internet. Universities were also targeted. Earlier this week, there were reports that the University of Calgary had received takedown requests and was warning faculty about posting their research online hit the academic blogosphere.
According to Thomas Hickerson, Vice Provost and Librarian at the University of Calgary, the Canadian university received a letter from a firm called Digimarc, which identified 32 instances where they believed published versions of journal articles had been posted in violation of Elsevier's copyright. These unauthorized copies appeared on the personal pages of faculty, department, and lab class websites.
The University complied with the removal request -- and they weren't the only ones. Both the University of California-Irvine and Harvard University have confirmed to the Washington Post that they received similar takedown requests.
I think Elsevier is just asking you to follow the rules that you agreed to when you signed the copyright form.