Again, please pardon my inexperience.
I launched the debugger application by double-clicking it, and then used File > Open to select the Loader.swf file...
I did that, had the same problem, and got no error message.
I also noticed that I had a second copy of the Loader on my hard drive. Don't know if that caused a conflict or not. I deleted it.
I had been playing around with the custom codes, trying to update after I altered a skin. I think that may have something to do with my problem.
I did not mean to imply (but I did, sorry) that I had saved the character as vanilla.
But I did use the feature to look at the paths, and noticed the BG path was not found.
I then checked the custom character code, and found the section referring to the BG to be corrupted.
I changed the background, did not 'save' the custom character as vanilla, generated a new character code, copied it, and used it to replace the custom code in the character mod folder. That seemed to do the trick. It is still working.
I don't know if this makes any sense from a programming standpoint, but it seems to have solved the problem. If it recurs, I will run the debugger (now that I know which one to use), and post the results, if any.
Again, thank your for your time, advice, and dedication.
EDIT: I created a new character folder and had the same issue. I checked settings. I noted that settings had flagged 'Load Last Code' on start. I set that to 1 "off" and now everything is fine again.