Internal compiler error System.Security.Permissions.SecurityPermissionAttribute is obsolete

I'm getting t$$anonymous$$s error when trying to build for the webplayer and I"m not really sure why. The full error is below. I thought it might be due to using sockets, so I ifdefed all my socket use out, but still get the error.

Internal compiler error. See the console log for more information. output was:warning CS0618: System.Security.Permissions.SecurityPermissionAttribute' is obsolete: CAS support is not available with Silverlight applications.' warning CS0618: System.Security.Permissions.SecurityAction' is obsolete: CAS support is not available with Silverlight applications.' error CS0617: `SkipVerification' is not a valid named attribute argument. Named attribute arguments must be fields w$$anonymous$$ch are not readonly, static, const or read-write properties w$$anonymous$$ch are public and not static G:\Unity_3_5_3\Editor\Data\Mono\lib\mono\unity_web\mscorlib.dll (Location of the symbol related to previous error)