Garmin Express may display the error message "Some files could not be uploaded to Garmin Connect" followed by "you may want to manually remove these files from your device". The corrupt files that this refers to are the .fit files that are recorded by the GPS alongside the gpx files.
.fit files are used by Garmin Connect for the Health Stats recorded during an activity.
You need to delete the corrupted file from the GPS internal storage using the Windows or Mac File Explorer. You cannot delete them through Basecamp.
Once you have located the Garmin Internal Storage in the relevant File Explorer (denoted by a blue triangle), Double click on the word 'Garmin' and find the 'Activities folder'
Having opened up the Activities folder, find the relevant corrupt .fit file/s and delete them. There is no 'repair facility'.
WE URGE GREAT CARE IN DOING THIS AND THIS IS DONE AT YOUR OWN RISK. WE DO NOT ACCEPT LIABILITY SHOULD YOU DELETE THE WRONG FOLDER OR FILE (it is useful to have the corrupt message window open at the same time so that you can compare the files to identify the corrupt file/files or make a note of them before proceeding).
Once you have deleted the corrupt file/s, disconnect the GPS and then reconnect the GPS and the GPS will be read by Garmin Express in the normal way