Error in application

Question

HI,
How to solve this problem ? Although i downloaded nothing still says "This assembly may have been downloaded from the Web." Why is it so ? Where to find the unblock button as mention below, I couldnt find this thing

Error  1  Could not load the assembly file://\\MCNSERVER2\UserProfiles\mspanwar\My Documents\Expression\Blend 4\Projects\Chatting application\Chatting application\obj\Debug\Chatting_application.dll. This assembly may have been downloaded from the Web.  If an assembly has been downloaded from the Web, it is flagged by Windows as being a Web file, even if it resides on the local computer. This may prevent it from being used in your project. You can change this designation by changing the file properties. Only unblock assemblies that you trust. See http://go.microsoft.com/fwlink/?LinkId=179545 for more information.  Chatting application.