Error with Competitor in Opportunity

Hi Experts!

I'm facing a problem when I try to assign a Competitor at header level into a Opportunity.

The CRM Web Ui performs the next message:

I set the next customizing into the Sales Transaction:

When I click Back into the button to return to the principal opportunity page, the next message appears:

Is important to say that when I try to select any option into the "Competitors" Page all the fields are empty, and I don´t have any option to select  values in the list box. I have some  Competitors (BPs) created but they don´t appear.

Anybody knows what is the problem?

Thank you so much for your help.

Maria.