$selection Variable is not an array or empty

Regards,

I've been working with this module an so far work's awesome, however I've run into an error, the dropbox feature doesn't let me add more than one term, even when i put the "Limit the number of selections" on 0.
After much work i realize that the parameter $selection on the function _hierarchical_select_dropbox_generate is empty or not an array sometimes, checking the log i get next error:

"Message Invalid argument supplied for foreach() in /var/www/sites/all/modules/contrib/hierarchical_select/hierarchical_select.module on line 2112."

so everything would work perfect but i cant add more than one term, and its frustrating, i have been dealing with this since 2 days ago, please if anybody can help i appreciate it.