I tried finish trailhead challange and I did prework and working correctly when I did last chalange and want check this then I got this strange error. I can't find any ifnroamtion on this error. I also create new Playground but it the same problem. 

"Challenge not yet complete in Cunning Panda Playground
We can't check your work because something in your org prevents creating and updating account and opportunity records. Check the settings and configuration of your org. Make sure you can create and update account and opportunity records. Then click Check Challenge again."

https://trailhead.salesforce.com/content/learn/modules/custom_metadata_types_dec/cmt_formulas