Support » Plugin: Autoptimize » Output bufferring error

  • Resolved dm4n


    Hi. Thanks for this plugin. I installed on latest WordPress core and it did seem to speed loading time but then got the output bufferring error:

    “Fatal error: Unknown: Cannot use output buffering in output buffering display handlers in Unknown on line 0”

    But interestingly, if I reload the page – the site will load ok.
    Plugins I’m using include W3 Total Cache, WP Super Cache, Deferred Javascript and BulletProof Security.

    Thanks for any assistance.


Viewing 6 replies - 1 through 6 (of 6 total)
  • Plugin Author Frank Goossens


    that’s a nasty bug to identify & fix dm4n …

    some questions:

    • does the error occur only once and then goes away forever, or does the error (occasionally) return?
    • can you disable all other plugins and see if the problem goes away? if it does, can you systematically enable other plugins to identify which one conflicts?
    • can you provide (copy/paste) the output buffering settings from you php.ini and/or the ob-related output of phpinfo()?
    • can you check what the amount of memory is that is allocated to php?


    Hi frank,

    Thanks for prompt reply.

    1. The error occurs when the plugin is activated and persists but is intermittent – 1st load brings up the error msg, 2nd load of the site on Safari loads ok. Resetting Safari (clearing browser cache etc) and the cycle recurs.
    2. output_buffering = Off in php.ini
    3. 256mb memory allocated to php
    4. Have yet to do the plugin deactivation test – FYI the site is using 16 active plugins from 42 installed (still experimenting with the site)


    Plugin Author Frank Goossens


    Thanks! Can you (next to toggling plugins to see if there is anything external to Autoptimize interfering) also try to change the Autoptimize settings and see what happens?

    • only “Optimize HTML”
    • only “Optimize JavaScript Code”
    • only “Optimize CSS Code”
    • Optimize HTML + JS (not CSS)
    • Optimize HTML + CSS (not JS)
    • Optimize JS + CSS (not HTML)
    • Optimize HTML + JS + CSS

      Hello @dm4n, from what you mentioned above in regards to the plugins you are using. You mentioned W3 Total Cache and WP Super Cache. Are you using both cache at the same time? If you are then that can cause a conflict between both plugins and Autoptimize.

      Kind regards

      I think that’s right – the error occurred if WP Super Cache needed to write to the .htaccess file and I wiped the caches before allowing the plugin to write.

      Also, I’m not using Bulletproof plugin at the moment.

      Since figuring that out – the error hasn’t reoccurred.


      Plugin Author Frank Goossens


      Great! Thanks for the support (mbrsolution) and feedback (dm4n)!

    Viewing 6 replies - 1 through 6 (of 6 total)
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