Hi again,
I have a partial answer to my own question but it isn't solved yet. Here is what I discovered: If you choose items from ONLY the Prediction Parts (like Name, MTBF Predicted, Category, SubCategory) and then DON'T transfer anything to the "Selected Fields" window in the "Specify Data Grouping" window then you will get a report.
If you transfer even one thing to the "Selected Fields" then you get the spurious error message that your report contains data fields from System Tree Items now.
So the workaround is this: Don't put anything in the "Selected Fields" window in the Wizard.
This still doesn't fix the problem of trying to display (say) both the MTBF from Prediction Parts and MTBF from the phase. According to the help file you can add things from other Table types to your report.
Regards,
Jack Davis