Yes, this is a common problem I see on the forum so I wrote an additional section in my new book on how to handle this (page 362).

I think the problem you are having is that you set the link to the ?PM field and are now trying to remove it. If so, you went just a bit too far. What you need to do is when you are linking to the subreport and CR is 'suggesting' that you link to the ?PM field, then click on the drop-down box and link to the subreport field directly. DON'T use the ?PM field that CR is showing in the dialog box. Just click that drop-down arrow and pick the correct field instead. When you close the dialog box, the appropriate fields will be linked and the ?PM field will never get created.

Re testing the subreport, if you double-click on the subreport in design mode and open it in it's own tab, then you can click the preview button to test it independently. I haven't done this in while and I remember something quirky happening with it that caused a problem, but I don't remember the exact circumstances. Give it a shot and let us know it it worked.

Interesting. When fields aren't listed in the dropdown box, that means that their data type doesn't match the data type of the field being linked to in the main report. For example, if the main report is linking with a string field, then only existing string fields will be listed from the subreport. Otherwise, the fields should be shown there.