Backup and restore

Hi,
i restored a Moodle 1.9 site from a MySQL dump, then upgraded it to Moodle 2.2.
it seems to work fine, but when i create a course on the Moodle 2.2 and try to backup the course, an error like below occurs. Any hints?

[Mon Apr 16 16:06:44 2012] [error] [client xx.xx.xx.xx] Default exception handler: error/baseelementchildnameconflict Debug: \n* line 99 of /backup/util/structure/base_nested_element.class.php: base_element_struct_exception thrown\n* line 152 of /backup/util/structure/base_optigroup.class.php: call to base_nested_element->check_and_set_used()\n* line 108 of /backup/util/structure/base_nested_element.class.php: call to base_optigroup->add_used()\n* line 173 of /backup/util/structure/base_nested_element.class.php: call to base_nested_element->check_and_set_used()\n* line 57 of /course/format/grid/backup/moodle2/backup_format_grid_plugin.class.php: call to base_nested_element->add_child()\n* line 55 of /backup/moodle2/backup_plugin.class.php: call to backup_format_grid_plugin->define_section_plugin_structure()\n* line 146 of /backup/util/plan/backup_structure_step.class.php: call to backup_plugin->define_plugin_structure()\n* line 363 of /backup/moodle2/backup_stepslib.php: call to backup_structure_step->add_plugin_structure()\n* line 86 of /backup/util/plan/backup_structure_step.class.php: call to backup_section_structure_step->define_structure()\n* line 153 of /backup/util/plan/base_task.class.php: call to backup_structure_step->execute()\n* line 103 of /backup/moodle2/backup_section_task.class.php: call to base_task->execute()\n* line 148 of /backup/util/plan/base_plan.class.php: call to backup_section_task->execute()\n* line 106 of /backup/util/plan/backup_plan.class.php: call to base_plan->execute()\n* line 304 of /backup/controller/backup_controller.class.php: call to backup_plan->execute()\n* line 111 of /backup/util/ui/backup_ui.class.php: call to backup_controller->execute_plan()\n* line 89 of /backup/backup.php: call to backup_ui->execute()\n, referer: http://foo.bar/moodle/backup/backup.php

[Mon Apr 16 16:06:44 2012] [error] [client xx.xx.xx.xx] Potential coding error - existing temptables found when disposing database. Must be dropped!, referer: http://foo.bar/moodle/backup/backup.php