Could not securely load assembly (Unity 4.5.1 + Facebook Unity SDK 5.1)

Question

I've just updated Unity from 4.3.4 to 4.5.1 and got this error with Facebook Unity SDK 5.1:

Could not securely load assembly from https://integrated-plugin-canvas-rsrc.fbsbx.com/rsrc/unity/lib/sdk_5.1/CanvasFacebook.dll

I tried the fix explained in Unable to verify assembly data; you must provide an authorization key when loading this assembly but was unable to comment (not enough reputaion) so had to ask a new question.

            string key =    "B8GvecdX0rQ47kzhCEwlrRzYKA8LKeiZxy1HI3HfnhdgUATvBwQQViji8ot44dADM55QuHk5+hwrLso" +
                        "au32IDmRDQTclMSsTsIywGRo/nE5vbmRMMIECYXBFhliz+kvK0RWZ57XPxw0s7YhGnNLav0EE2QH/m+9a" +
                        "jlLOY+2ckxSoSEHLpotllyZLktRK+oFiDPvmzXLDUMOnwK9RFRSh2VBmoyWTZx8BYqWjqug3kAljJk/Xw" +
                        "TYZT9Ie+HvzLO5DBSqMNYbEX03WaNfpaq9GKBF/Oz37AHelf1Es36amP1v2Aut3nmIk2xxN6zwzBXyEyw" +
                        "90vJ/O8suikU+8kDDbZA==";

        var assembly = Security.LoadAndVerifyAssembly(www.bytes, key);

Note that I added the fix code into the UNITY_4_5 section.

Is the key now wrong as it was given back in March?

I should note that I only see this error in one project. I have another project that also uses the Facebook Unity SDK but I don't see the error in that one.

UPDATE:

As of Monday 30 June the original issue seems to have been resolved. There's now no problem loading the assembly via the original code.

UPDATE 2:

Actually I've seen the secure load fail a few times since, but not always.