Thanks to some wonderful people in this forum, I have been able to locate the source of the problem of errors on saving.
There is a limit (NOT imposed by CCWPO) on the size of the data for the pattern. That limit is 1 megabyte. Images that are scanned and imported can easily exceed this limit. In a problematic library that TerryT was kind enough to send me, I found two that were well over that limit. Deleting them from the library cured the problem.
Now that I know the issue, I will investigate ways to resolve it. Until then, if you import PNGs, make sure they are less than 1 meg in size. (If larger than that, you probably need to reduce the resolution, anyway. Designer can only handle about 200 DPI. Anything over that is wasting memory and disk space.)
If anyone is having issues using the sample that I provided, please private mail me with some details (problem, errors, XP vs VISTA).
Thanks for your patience AND all the great words of encouragement and appreciation I have been receiving.