Nacho-
You're not missing anything, I think. There is a bug with itemTips. The following is quoted from the MS KB:

PRB: ItemTips = .T. Causes Error When in Private DataSession
Last reviewed: December 12, 1997
Article ID: Q165889 
 

The information in this article applies to: 
Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a 


SYMPTOMS
In Visual FoxPro 5.x, the Listbox control with the ItemTips property set to ".T. - True" causes a "Cannot access the selected table" error when the DataSession property of the Form is set to "2 - Private Data Session." 



RESOLUTION
Set the form DataSession property to "1 - Default Data Session." 
 

>There are a problem with itemtips(.T.) of listbox and private datasession. After the form is showed, when you pass the mouse over the listbox, the error "can't acess table" is up. If the itemtips is .F. all works OK.