Tasks Problems over and over and ... over again

Hello everybody,

I have problems importating my tasks, it just don't work the way it should :
i'm still not able to obtain a good way to migrate tasks and events from another crm, I guessed, that for you, during the matching of fields

what_id = parent_id = accounts id or = NULL if there is no account linked (directly) to the task and a contact linked to the task
who_id = contact_id or = account_id if there is no contact linked to this task

The issue is that i'm still getting an error, the tasks appear, they are linked to accounts or contacts that they should be linked to, but i can't access them !!!!
If i click on it i get an error and no way to access the task
However it's here in your database because when i try to export it via export all data, i get the right tasks, the right description (which i can't see cause i can't access the tasks).
Would anybody please answer me on how to solve this issue !!!!!

thanks and regards

ogirardo.