How do remove this....

[Angeltheartist]

Ever since I updated with the Dream Pack update This pop ups at start up , once I click OK I can continue.What can I do to resolve .

 

[Stereo]

Those skins ui_skin.json have errors in them (missing data or invalid code), you can fix the json (see eg. http://jsonlint.com/ ) since it's a text format, or delete the skin.

 

[gamer19]

I think there's even simpler solution - you can just delete those JSON files (alt-tab when you got that message and track those troublesome skins) many skins are already without JSON files and they working just fine.