Suppose we have the following seam-beans.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://java.sun.com/xml/ns/javaee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:s="urn:java:ee" 
       xmlns:r="urn:java:org.example.reports">
 	<r:Report>
 		<s:modifies/>
  	</r:Report>
</beans>

But no org.example.reports.Report in the project classpath.

Seam config validation will mark <r:Report> as unknown type. That's correct.
Create org.example.reports.Report class.
The seam-config.xml should be re-validated and the problem marker disappear.