Cannot Delete Contents of Sandboxes - Why? How?

Admittedly this is with Sandboxie 5.30 (registered) 64-bit under Windows 7 Sp1 in a Standard User account; but as first noticed today, I cannot delete the contents of two of my five sandboxes.  Below are the sandboxes and the files remaining in one of them.  (I've set the sandboxes to automatically delete contents when their respective programs are closed.)

Here is the error message I get when I try to delete contents:

And here is the file structure in C:/username/Sandboxie that I suspect may indicate where the problem lies:

My questions are two:

1) Does this likely indicate some sort of virus-infection attempt, fortunately within the sandbox, or some other kind of problem?

2) Can I simply delete the non-empty parts of the directory structure (perhaps in safe mode or at a command line as Administrator) and be done with it, or will this likely cause some other problem?

Thanks in advance for any suggestions. -- jclarkw