This problem was caused by WP Fastest Cache plugin the famous cache plugin with over 1 million active installations. Disabling all the options and testing one by one I’ve found that the problem happens when I flag one of these options:
- Minify Css
- Combine css files
- Combined js files
This work is really awesome and very useful. But…
It may happen that the minification process brakes everything and causes the mysterious error: Fatal error: Unknown: Cannot use output buffering in output buffering display handlers in Unknown on line 0.
These options normally works really fine, I’ve uses WP Fastest Cache plugin on many WordPress installations, I trust their developers!
I’ve found that the problem is within the script inclusion, I use inclusion directly in the
footer.php or in
header.php of my themes, like these:
And the problem happened due to the “
/” chars in the version parameter (I sometimes put the date as version parameter). Removing the “
/” solved the issue.
I don’t know if someone else ever found this problem.