I had the same error message, but I had previously gotten PlayThru to work on my site with my Kunena forum registration. I was puzzled when I went back a few months later to see that my Contact Form didn't work. Followed all my previous steps and found one more place that needed attention. Here's that last step that got it working in my core Joomla Contact Form:
1) Went to my Contacts through the Contact Manager.
2) Found the Contact that works with my form and checked/selected the box. Not Edit.
3) Then clicked the Options icon in the top right of the admin page,
4) Went to the FORM tab. The first selection is a drop-down menu. Here I chose PlayThru instead of default. Even though I had already chosen PlayThru as default in Global Config, it didn't work.
5) Click SAVE and Close, then refresh the Contact Form page.
Hope this helps!
Great plugin - Thanks!!
I am also using a JS Wright Template, Impacto on Joomla 2.5.11