What I do ... connect the unit to the computer; open the unit as if it were a separate drive; copy the GPX file and then try and paste it into new files; I then get the 'full/no memory' message.
I don't know about the 200 but with many Garmins there's a distinction between the 'memory' as on the SD card or even on the virtual drive that you see when connecting the GPS, and the 'device memory' which is actually where the active GPS data is held, and which is not directly accessible from a computer.
In other words, you copy stuff onto the card (or the virtual drive, same diff) and then when the GPS is disconnected and restarted, this stuff is synchronised into the device memory. The synch process only works one way, so if you then delete stuff from the card/virtual drive, that does
not also delete it from the device memory.
To clear the device memory you may have to do it via the GPS menus - deleting Tracks, Courses, Waypoints etc. Older models had a handy 'reset' facility which made all this easy, but this seems to have been lost on newer models (there's still a 'reset' but it is more of a 'wipe all settings' thing - not what is wanted!)