Has one of your parts got settings to start new page or restart page numbering?
Yes, the following subsummary part has New Page checked, although I have tried it with all different configurations. Since this was such a simple report, I just redid it, having wasted an hour trying to figure out what was wrong. I have probably 30 other subsummary reports and they all work fine. Strange.
Thanks for trying to help, Lyndsay. I felt so stupid posting such a basic question.
Another thought I had was that one of the parts might be big enough to push the following parts to the next line...
... and don't feel silly posting... I like to say "it is always a dot or a comma that causes the problems which you spend hours trying to resolve" (I do a lot of web-coding but same principle applies with FM)