I do not see any obvious problems with the code. To help track this down,(1) try printing each row to stdout to see if the record is even returned, (2) see if the mkdir returns an error code.

Also, you mention IO as being in $db[0] at the beginning of your post, but in $data[1] in the second snippet; check that you have the correct field number.

One final thought: if your DB never shows any records with IO, how do you know it was ever properly entered into the database?