Fatal Error with Visual Composer

When I want to use the “Edit with Visual Composer” option in Pages, I get this error..

Fatal error: print_r(): Cannot use output buffering in output buffering display handlers in …. etc, etc.

Please see print screen image. I have changed the contrast of it so it coulb me more readable…it seems that wants to load something, but there it stays.

Thanks very much
Best Regards

Juan