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?
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.phpfor thedomain_mapping_plugins_uri()function (around line 650), short-circuit that function by just returning$full_urlwithout running through its other routines.This should fix the problem.
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