I have set up a multisite (sub directories) and all my plugins/CSS was working fine. Then I added domain mapping and managed to point a domain example.com to a site ID 4. All still working fine.

However, when I make example.com for site ID 4 'primary', the CSS seems to break. My plugins (e.g. responsive slider) no longer works, my CSS also. The moment I un-check the 'primary', all seems to work fine.

Any ideas what could be happening?

  • How did you go with this user32062?
    – Tim Malone
    Commented Jul 6, 2016 at 3:59

2 Answers 2


This is an old question, but I just ran into this same issue and found the problem: the MU Domain Mapping plugin is using a deprecated constant, PLUGINDIR, to remap the plugin directories on the mapped domains.

The plugin seems to be very vaguely developed nowadays (and no releases have been out for a year), so I just edited my copy of the plugin directly. In domain_mapping.php for the domain_mapping_plugins_uri() function (around line 650), short-circuit that function by just returning $full_url without running through its other routines.

This should fix the problem.

  • 2
    the domain mapping plugin should be considered deprecated in my experiance as well Commented Apr 13, 2016 at 3:34
  • Yes, agree! It definitely needs some attention to bring it up-to-date with modern WP. Fortunately, my use case is only for dev domains (production won't need it), but others aren't so fortunate.
    – Tim Malone
    Commented Apr 13, 2016 at 3:37
  • @TimMalone I also use the DM plugin for development too. It's very useful in this regard. Commented Feb 26, 2017 at 5:52

Check out these instructions, Debugging a WordPress Network. That kind of problem is usually caused by a configuration error in the .htaccess file. Check also this page, Multisite configuration fails with css/js files

  • 2
    this is a comment, not an answer. An answer should give a "solution", suggesting additional debuging steps belongs to comments Commented Apr 13, 2016 at 3:33

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