Most likely a file configuration error. Check the following files and make sure they are all configured correctly. I would use the Seam Documentation and just copy and past their examples--that way you can understand what each setting does.
%EJB3_JAR%/META-INF/persistence.xml
%EJB3_JAR%/seam.properties
%WAR_JAR%/WEB-INF/web.xml
%WAR_JAR%/WEB-INF/faces-config.xml
you have to have seam.properties even if empty. This is the way seam identify the module with seam components (ejb jar)