Same issue
WordPress 3.9 included a large update to the TinyMCE WSYIWIG editor and the coding for adding buttons to the toolbar changed. Suspect it relates to that.
The shortcodes still work however and its not too hard to construct them manually.
Thanks for the report; I’ve got an update coming out soon that will restore the toolbar button for WordPress 3.9+.
https://bitbucket.org/figureone/insert-pages/commits/5fbc3d755ef39dec4cd8c3be3b7437cce2b60293
Cool thanks, this really is one of those plugins that I cant live with out now.
The base functionality is really great, getting the insert button working again would be even greater.