Can you please try recycling the application pool, as it looks like the data caching might still be referring to the media items previously present in that particular library. If any issues persist, please do not hesitate to let us know, we'll be glad to help.
All the best,
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items