Strange Compile error , my Project Assemby cannot be found Pin

Question

 Error 2 Assembly 'lab1' was not found. Verify that you are not missing an assembly reference. Also, verify that your project and all referenced assemblies have been built. D:\wpf\lab1\lab1\Window1.xaml 4 18 lab1

I am using the following code in order to use my user control in my project but the error mentioned before occurs :

 xmlns:local= "clr-namespace:lab1"

PS: my Project and also Solution Name is lab1 so i am referencing to my project


please tell me what should I do, thank you