Error caused by misplaced parenthesis in drupal_set_message() function with error option.

An error with installing the databases (not visible here, the problematic database failed silently. The duplicate key error below has to do with a database not being deleted on uninstall.)

* user warning: Duplicate entry '1' for key 1 query: INSERT INTO placement_regions (rid, region) VALUES (1, 'Top left'), (2, 'Top right'), (3, 'Bottom right'), (4, 'Bottom left') in /sites/jonassoftware/www/includes/database.mysql.inc on line 172.
* warning: Invalid argument supplied for foreach() in /sites/jonassoftware/www/includes/common.inc on line 744.
* warning: strtr() [function.strtr]: The second argument is not an array in /sites/jonassoftware/www/includes/common.inc on line 759.

Looked up line 744...

That's the T function!

it was this:

<?php
    drupal_set_message(t('Placement module installation was unsuccessfull. Necessary database tables should be created by hand.', 'error'));
?>

instead of:

<?php
    drupal_set_message(t('Placement module installation was unsuccessfull. Necessary database tables should be created by hand.'), 'error');
?>

Tricky misplaced parentheses!

Resolution