Probably you see something like
An error occurred while launching/running the application.
Title: eXist XML-DB client
Vendor: exist-db.org
Category: Security Error
Unsigned application requesting unrestricted access to system
Unsigned resource: http://localhost:8080/exist/webstart/stax-api-1.0.1.jar
while the exception reads like:
JNLPException[category: Security Error : Exception: null : LaunchDesc:
<jnlp spec="1.0+" codebase="http://localhost:8080/exist/webstart/"
href="http://localhost:8080/exist/webstart/exist.jnlp">
The solution is to re-sign the jar files:
build.sh -f build/scripts/jarsigner.xml jnlp-unsign-all jnlp-sign-all