When I print a narrative report it has several (NEED TO DEFINE SENTENCE:Hobby). What does it mean? How can I correct it?

It means you imported a GEDCOM file from another program that had user defined facts in it (in this case "Hobby"). RootsMagic does not know how to write a sentence for that fact type.

Do "Lists > Fact type list" from the RootsMagic menu, then find that fact type in the list. Highlight the fact type and click the "Edit" button. Near the bottom of the edit dialog is the place to enter the "sentence template" which tells RootsMagic how to write a sentence for that fact type.

You can press the F1 key for help on that screen which will tell you how to do this.