I accidently corrupted the directory for the GPX folder on my 400t. I wasn't able to fix it with Windoz. I went to command prompt (run | cmd) and navigated to the Garmin | GPX folder. (in my case, D:\Garmin\GPX) I couldn't open it there either. I ran chkdsk command there and it returned that errors were found, but not corrected, and to run chkdsk /f.
I did that, and the return was that the directories were truncated in order to set the file structure right. I saw that GPX was indeed missing. I did an md GPX. command at D:\Garmin, and the (empty) GPX folder was created.
Typed exit to go back to windows, and did a shutdown and remove. I turned on the unit, and everything looked fine. No caches, of course. Re-mounted the garmin, and copied one large GPX file to the GPX folder. De-mounted, and turned on the Garmin, and voila! back in business.
Jim