The problem could be caused by customized theme. If you use not 'default' theme package you should make following actions:

Move file app/design/frontend/default/default/layout/mppinterest.xml to app/design/frontend/[YOUR PACKAGE]/[YOUR THEME]/layout

And also move folder app/design/frontend/default/default/template/mppinterest to app/design/frontend/[YOUR PACKAGE]/[YOUR THEME]/template/

After that please clear cache and everything should be ok. If you will have troubles after that please contact our support team.

With best regards,
Igor Goltsov