I went into one of my courses, went to the gradebook and did a grade export. I created a second course and attempted to import the grades into that course. The following was output.

Notice: Undefined property: stdClass::$mapping_1 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
Call Stack

1. Time Memory Function Location
   1 0.0010 338192 {main}( ) ../index.php:0
   
   ( ! ) Notice: Undefined property: stdClass::$mapping_2 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
   Call Stack
   # Time Memory Function Location
   1 0.0010 338192 {main}

   ( ) ../index.php:0

( ! ) Notice: Undefined property: stdClass::$mapping_3 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
Call Stack

1. Time Memory Function Location
   1 0.0010 338192 {main}( ) ../index.php:0
   
   ( ! ) Notice: Undefined property: stdClass::$mapping_4 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
   Call Stack
   # Time Memory Function Location
   1 0.0010 338192 {main}

   ( ) ../index.php:0

( ! ) Notice: Undefined property: stdClass::$mapping_5 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
Call Stack

1. Time Memory Function Location
   1 0.0010 338192 {main}( ) ../index.php:0
   
   ( ! ) Notice: Undefined property: stdClass::$mapping_6 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
   Call Stack
   # Time Memory Function Location
   1 0.0010 338192 {main}

   ( ) ../index.php:0

( ! ) Notice: Undefined property: stdClass::$mapping_7 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
Call Stack

1. Time Memory Function Location
   1 0.0010 338192 {main}( ) ../index.php:0
   
   ( ! ) Notice: Undefined property: stdClass::$mapping_8 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
   Call Stack
   # Time Memory Function Location
   1 0.0010 338192 {main}

   ( ) ../index.php:0

( ! ) Notice: Undefined property: stdClass::$mapping_9 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
Call Stack

1. Time Memory Function Location
   1 0.0010 338192 {main}( ) ../index.php:0
   
   ( ! ) Notice: Undefined property: stdClass::$mapping_10 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
   Call Stack
   # Time Memory Function Location
   1 0.0010 338192 {main}

   ( ) ../index.php:0

( ! ) Notice: Undefined property: stdClass::$mapping_11 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
Call Stack

1. Time Memory Function Location
   1 0.0010 338192 {main}( ) ../index.php:0
   
   ( ! ) Notice: Undefined property: stdClass::$mapping_12 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
   Call Stack
   # Time Memory Function Location
   1 0.0010 338192 {main}

   ( ) ../index.php:0

( ! ) Notice: Undefined property: stdClass::$mapping_13 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
Call Stack

1. Time Memory Function Location
   1 0.0010 338192 {main}( ) ../index.php:0
   
   ( ! ) Notice: Undefined property: stdClass::$mapping_14 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
   Call Stack
   # Time Memory Function Location
   1 0.0010 338192 {main}

   ( ) ../index.php:0

( ! ) Notice: Undefined property: stdClass::$mapping_15 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
Call Stack

1. Time Memory Function Location
   1 0.0010 338192 {main}( ) ../index.php:0
   
   ( ! ) Notice: Undefined property: stdClass::$mapping_16 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
   Call Stack
   # Time Memory Function Location
   1 0.0010 338192 {main}

   ( ) ../index.php:0

( ! ) Notice: Undefined property: stdClass::$mapping_17 in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 180
Call Stack

1. Time Memory Function Location
   1 0.0010 338192 {main}( ) ../index.php:0
   
   ( ! ) Notice: Undefined property: stdClass::$mapfrom in /home/andrew/Desktop/git/moodle_mygithub/grade/import/csv/index.php on line 184
   Call Stack
   # Time Memory Function Location
   1 0.0010 338192 {main}

   ( ) ../index.php:0

user mapping error, could not find user!