I can't seem to load more than two courses onto my 530, when I try download a third it just deletes one of the first two.
What is the source of the courses, did you create them, are they the same name? (name can be tricky as the "file" name can be different to the course name label inside the TCX/GPX/Fit and the type extension will be dropped when the course file is converted on the device into a .FIT
The Garmins use only like the first 12 letter of the course name.
The course name is inside the file (so, it's not the name of the file). If it's a gpx or tcx file, you can edit the file to change the name using a text editor (lie notepad++).
If the difference in the name is after the 12 letter, the second one will overwrite the first.
Keep the names short.