How do I delete files from Time Capsule?

I have tried to move some files to my Time Capsule disk (NOT a Time Machine backup) in the Data folder. The transfer was interrupted and now I can't delete the files there?

I get an error message saying I don't have permission, but all is set to read & write. I can see several similar issues from other users previously but with no usable solution. What is going on and how do I delete these files?