Issue in CRM2013 around Add to Markting List button on the contact form.
In a customer i was having a issue with the ‘Add to Markting List’ button on the contact form, but it was giving that error only in a new form that we have created. So, after research, I found on this post the workaround or fix to it. https://community.dynamics.com/crm/f/117/t/118904.aspx
I added the list of cases to the form and i’ve hidden the tab, and now is working.