Upgrading forum to 4.1.19: Key column 'field_' doesn't exist

[Ibai]

I am getting this error while upgrading to 4.1.19 and cannot complete the upgrade:

1072: Key column 'field_' doesn't exist in table 
/home/fmsite/public_html/applications/downloads/setup/upg_101088/upgrade.php::46

any ideas? I also opened a ticket on this but in case that anyone had this issue... My community is broken right now  

cheers