Migrate to target framework 4.5

Question

Hi,

 

I am working on a solution that have 50 project and  target is framework 3.5 of all.

Now i need to add system.xaml in main project of this solution.

That's why change target of main project to 4.5.

Finally i am going to build , it has not been successfully build.

 

Help anyone.

 

Thanks in advance!!!