FileLoadException in vs 2010 xaml designer with SLite 1.0.66
I'm a bit late to the party with this response, but having spent most of the morning with the same issue (albeit with a different DLL to the OP), I can provide a solution for anyone else unfortunate enough to come across this puzzling problem.
The error message suggests that you are trying to load an assembly from a network location or the web - a bit misleading, but also kind of true.
The issue is caused by Windows 7 "knowing" that the DLL has been downloaded from the web, even though it might have been inside a zip file at the time. The file is therefore marked as being potentially unsafe. To resolve it, right-click the DLL, choose Properties, then click the "Unblock" button. Voila! (Alternatively you could unblock the zip file prior to extracting the files within).