And one more:
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I found in java console log following string:
network: Firewall authentication: site=<fqdn>/<ip>:80, protocol=http, prompt=, scheme=ntlm
Applet can't connect to server due to security authentication.
There is the solution I found in Internet:
Enabling anonymous authentication on the virtual folder always solves the problem
Does customer have IIS?
Here I found how we can allow anonymous authentication for IIS:
http://soft-haus.com/blog/2009/12/04/network-firewall-authentication-site-protocolhttp-prompt-schementlm-how-to-get-applets-loading-in-linux/
..
Simply have a look at the Java Console log and check if this applies.
Greetings
Siggi