Here's how to reproduce this error on a panel node page with IPE:
1. Click "Customize this page"
2. Click "Cancel"
3. Click "Customize this page" again.
I get a 403 error on the third click, forcing me to reload the page in order to get into the IPE again.
Comments
Comment #1
nackersa commentedWe were experiencing this problem as well. We were able to create a patch that seems to have fixed the problem (for us). See http://drupal.org/node/1613402
Comment #2
ordermind commentedGreat, I'm closing this then :)