Event ID 2548 – SharePoint Server Search
I have built a new SharePoint 2013 environment and after provisioning a new Search Service Application the following was regularly being logged in the Application Event Log:
Content Plugin cannot be initialized – list of CSS addresses is not set
After a fair amount of Googling and looking through logs I learned that this was caused by the Search Service Application not being fully provisioned. After removing and recreating the Search Service Application these errors went away.