When I pop the micro sd card in a reader and try to access the file on my computer I get a "problem opening the file...the file you opened has some invalid characters." Sometimes the first couple of lines will open correctly, but garbage for the rest.
I checked the card, it is formatted Fat16.
Your PC can't access the files on the SD card. Some application running on the PC can. It wasn't the PC that said "Problem opening file...". It was an application on the PC.
So, what application is doing the complaining?
What sketch is writing to the SD card on the Arduino?