1. Backup v2.3.11 - SQL, config_db.php, config.php, installed_extensions.php lang/linstalled_languages.inc
2. Uninstall all extensions.
3. Backup SQL again along with the said files
4. rename the frontaccounting folder.
5. extract latest mercurial build onto new frontaccounting folder
6. install FA to another dummy db.
7. compare the saved files (config_db.php, config.php, installed_extensions.php lang/linstalled_languages.inc) with the currently installed ones and make changes to use the old db.
8. Login to the 0 company and go to Setup -> Software Upgrade and force an upgrade.
Post your php.ini file along with the output of:
uname -a
php -m
Better still, VNC your desktop which can be chrooted into your cloud server.
Report Generator extension is broken / unsafe for FA v2.3.13+