I'm starting to get a handle on the problem, and it took building a new list to do so. But I still don't get what's going on.
Somehow SharePoint (or InfoPath, or both) is not letting go of old, obsolete error situations.
For instance, in the original problem, even after I deleted everything that could have caused the problem, it persisted.
So next I built a new list, and tested it column by column. At one point I added a concatenated value to a field, but I screwed up: I added it as a default value to an existing bound text box instead of a new Calculated Value control. The result was that the concatenated text went on forever and generated a time out when I Previewed the form. Oops.
I realized my error and corrected it-- but from that point on, I now receive this error:
Default values, rules or code may be running in an infinite loop. To prevent this, ensure that the default value, rule action or event handler does not update the data which causes the same rule action or event handler to execute.
So once again I stripped out any possible offenders (the original problem had already been fixed) but SharePoint refuses to acknowledge that the problem no longer really exists.
This has me completely stumped. It seems that SharePoint is "seeing" the old, error-afflicted form rather than the newly published one(s). Do you know if it's a SharePoint or InfoPath problem? Any idea how to correct this?