UI 4.6 mask not working in old project

I have old project started in earlier version of Unity and I need to create mask which will hide part of panel.
I'm creating new panel and canvas and panel is created. I create another panel as child of previous which is bigger then parent.
After adding Mask script on parent panel, nothing happens.
I have tried on existing scene but also tried to add new scene in this project but without success.

But, if I create new project, everything working as expected.
Also, everything is working just fine if I add those two panels and mask in example project (angry bots), so, something is wrong in my project.
When I create canvas with two panels and mask and save scene in new project (which is working fine), and if I copy this scene to my existing project, mask stop working. Enabling or disabling mask has no effect.

Can you advise me how to debug what is causing problem with mask only in old project.

Thanks in advance, Ivan

 

Yes...
Setting 24 bits and restarting Unity fix all issues...

Thank you...