After Effects - Unable to Access Resource

Hey folks, recently using After Effects beta, i'm getting a lot of this kind of error. Happens suddenly and I havent found anything online about it. 

The error happens with files in the project and other things that I don't understand.

It aways show up: "After effects beta warning: unable to access resource..." and then it freezes, I have to force quit. 

In this project of the print screen, it's only a layer with cc ball and fractal noise, but it already happened with file (psd, ai) and other names like on the print screen that I don't remember.