Backup your data then use the Panasonic SD Formatter do a "Full Overwrite" and Size Adjust to ON
Grab the latest RGF unofficial update from filetrip and then put your games and saves back and see what happens
Failing that try another MicroSD and clean the pins on the DSTT you could also spray a burst of compressed air into the slot 1 of your DSLite but remember that it should be a short burst and keep the can level otherwise something like liquid ice can be shot out potentially damaging your DS
If you can also try your DSTT in another DS / DSLite to rule out your DS as a issue