See Missing Codebase manifest attribute for:xxx.jar for an explanation for Permissions and Codebase. If you use ant, you can use the following to add the entries to the manifest:
<manifest file="${source}/META-INF/MANIFEST.MF" mode="update">
<attribute name="Permissions" value="all-permissions"/>
<attribute name="Codebase" value="${jnlp.codebase}"/>
<attribute name="Application-Name" value="${app.name}"/>
</manifest>
Java 7 update 45 broke my Web Start SWT application might also have some interesting information