Hi. I joined the forum just for this specific problem
Before even visiting, I did all the same things that jhoward did, and like hotrod I went back to v2.28.1091 and it works perfectly again.
When checking the contents of my default box after running ccleaner, it would say (when working properly) "There are 0 files and 1 folders in the sandbox."
But after running v2.29.1111 I had 54 folders and 158 files, so I don't know what ccleaner is missing.
My path (If this is what you mean ) is
C:Sandbox\Owner\DefaultBox\*.*
Let's get this fixed so that we Sandboxie users aren't stuck in v2.28 as new versions arrive