The error means your MySQL module is set to use only_full_group_by mode.
The elements of the error message include:
Error Number: 1055
Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column... ; this is incompatible with sql_mode=only_full_group_by
Filename: libraries/Datamapper.php(1) : eval()'d code(3) : eval()'d code
Line Number: 1348
Disable the only_full_group_by mode.
To do so, you can either run the following SQL command:
mysql> SET sql_mode=(SELECT REPLACE(@@sql_mode,'ONLY_FULL_GROUP_BY',''));
... or, if you have access to the server as a root user, edit the file:
... by looking for the line:
... and removing the value:
... from the line.
After the file is changed, save it. Then restart your MySQL service.