I can access the url from my browser ok (it asked me to download the file):
http://www.sun.com/software/appserver/dtds/sun-ejb-jar_3_0-0.dtd
Do you have internet connection for the computer where this was run?
There should be a DOCTYPE defined in each sun-*.xml and we use the public id of the DOCTYPE as the key to find dtd from local repository. For example, this is the DOCTYPE that should be used if you want to reference sun-ejb-jar_3_0-0.dtd:
<!DOCTYPE sun-ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Application Server 9.0 EJB 3.0//EN" "
http://www.sun.com/software/appserver/dtds/sun-ejb-jar_3_0-0.dtd">
The DOCTYPE is documented in the beginning of the dtd.
Only when we cannot use the key to find the dtd from local repository (for example, there is a typo in DOCTYPE), we will try to go to internet to get dtd.
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