Error Impossible WHERE noticed after reading const tables

hi, 

I'm trying to intall phpOpenTracker-1.5.0rc1. It's been a mixed success because, 
it working only for for some actions. 

I always get

Impossible WHERE noticed after reading const tables

when runnig ::get() actions. 

I've looked in my tables and the visitors_table is empty. 
it seems that ther are not logging action for the visitor info... 

the pot_documents table and  pot_accesslog  get updated on ::log(),
but that's about it...

ps. running in mysql_merge mode.

thanks in advance.