(1) I'd like to suggest an option to change the behavior of WPC when it is unable to find a wallpaper. Perhaps a tick in the preferences for "Ignore warnings" or "Skip warning dialog".
Currently, I think the dialog exists because WPC thinks that the user has removed too many wallpapers from their list and directs them to the filename cleanup utility.
For organization, I keep all my wallpapers on a central PC and grab the wallpapers from it over a wireless network. If I need to reboot/shut down the central computer, and the remote machine is still running, during the next cycle WPC gives the message "Unable to find an existing wallpaper after trying 10 times...." dialog which needs a response (press return). Sometimes, if this happened overnight, I will need to click through the box 20 times or more because of unattended cycling.
If the tick/option is added, the current wallpaper would then be displayed until the folder could be found on the next cycle (or some action by the user). The wallpaper not changing would be cue enough for the user who checked the box that something isn't working as intended.
(2) An alternate/additional idea is to change the behavior a bit. Currently when a filename is in the list, but the file is not physically there, WPC shows a blank (black) wallpaper. It would be nice if it could try again from the list (up to 10 times like it is currently) to display the next wallpaper, or to simply keep the existing wallpaper and not change it to a blank. This would make having to do upkeep (manually search/delete files from list) a little less often.
Both are minor annoyances to an otherwise great product.