We have a legacy program that was ported from Java 1.3 to Java 1.5. This application involves applets which worked fine before. After porting however, the applet would not load. However there are no errors or exceptions. The app would just try to load it forever. We tried to run it with Java 1.6 and poof! No problems whatsoever. Isn't Java 6 backwards compatible? So how come it would run in that version and not in 1.5?

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Java Console log for Java 1.5.0_19

basic: Registered modality listener
basic: Registered modality listener
basic: Registered modality listener
liveconnect: Invoking JS method: document
liveconnect: Invoking JS method: document
liveconnect: Invoking JS method: document
liveconnect: Invoking JS method: URL
liveconnect: Invoking JS method: URL
liveconnect: Invoking JS method: URL
basic: Referencing classloader: sun.plugin.ClassLoaderInfo@bb7759, refcount=1
basic: Referencing classloader: sun.plugin.ClassLoaderInfo@bb7759, refcount=2
basic: Referencing classloader: sun.plugin.ClassLoaderInfo@bb7759, refcount=3
basic: Added progress listener: sun.plugin.util.GrayBoxPainter@b0bad7
basic: Loading applet ...
basic: Initializing applet ...
basic: Starting applet ...
basic: Added progress listener: sun.plugin.util.GrayBoxPainter@ba9340
basic: Added progress listener: sun.plugin.util.GrayBoxPainter@1198891
basic: Loading applet ...
basic: Initializing applet ...
basic: Starting applet ...
basic: Loading applet ...
basic: Initializing applet ...
basic: Starting applet ...
basic: Referencing classloader: sun.plugin.ClassLoaderInfo@bb7759, refcount=4
basic: Releasing classloader: sun.plugin.ClassLoaderInfo@bb7759, refcount=3
basic: Referencing classloader: sun.plugin.ClassLoaderInfo@bb7759, refcount=4
basic: Releasing classloader: sun.plugin.ClassLoaderInfo@bb7759, refcount=3
basic: Referencing classloader: sun.plugin.ClassLoaderInfo@bb7759, refcount=4
basic: Releasing classloader: sun.plugin.ClassLoaderInfo@bb7759, refcount=3
network: Connecting <something>.jar with proxy=HTTP @ proxy/<ip address>
basic: Loading <something>.jar from cache
basic: No certificate info, this is unsigned JAR file.
Left START init()
Left END init()
Right START init()
Control start() Waiting for Left Panel to load...
Right START start()
network: Connecting socket://<ip address>:14444 with proxy=DIRECT
Control start() Waiting for Left Panel to load...
Control start() Waiting for Left Panel to load...
Control start() Waiting for Left Panel to load...
my HostName : <ip address>
Thread-19 Check : 
Thread-19 Check : Monitor : run : start
Thread-20 Monitor : Monitor: run() start
Control start() Waiting for Left Panel to load...
Control start() Waiting for Left Panel to load...
Control start() Waiting for Left Panel to load...
Control start() Waiting for Left Panel to load...
Control start() Waiting for Left Panel to load...
Control start() Waiting for Left Panel to load...

the last message goes on forever... and now with the working version:

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Java Console log for Java 1.6.0_15

basic: Added progress listener:   sun.plugin.util.GrayBoxPainter$GrayBoxProgressListener@1b000e7
basic: Added progress listener: sun.plugin.util.GrayBoxPainter$GrayBoxProgressListener@12611a7
basic: Added progress listener: sun.plugin.util.GrayBoxPainter$GrayBoxProgressListener@1807ca8
network: CleanupThread used 6 us
network: CleanupThread used 5 us
network: CleanupThread used 6 us
cache: Skip blacklist check as cached value is ok.
network: Cache entry found [url: <something>.jar, version: null]
network: Connecting <something>.jar with proxy=HTTP @ proxy/<ip address>
network: ResponseCode for <something>.jar : 304
network: Encoding for <something>.jar : null
network: Disconnect connection to <something>.jar
Reading certificates from 11 <something>.jar | <something>.idx
network: No certificate info for unsigned JAR file: <something>.jar
basic: Applet loaded.
basic: Applet loaded.
basic: Applet resized and added to parent container
basic: Applet resized and added to parent container
basic: PERF: AppletExecutionRunnable - applet.init() BEGIN ; jvmLaunch dt 330275 us, pluginInit dt 27768955 us, TotalTime: 28099230 us
Right START init()
basic: PERF: AppletExecutionRunnable - applet.init() BEGIN ; jvmLaunch dt 330275 us, pluginInit dt 27770563 us, TotalTime: 28100838 us
Left START init()
basic: Applet loaded.
basic: Applet resized and added to parent container
basic: PERF: AppletExecutionRunnable - applet.init() BEGIN ; jvmLaunch dt 330275 us, pluginInit dt 27779332 us, TotalTime: 28109607 us
Left END init()
basic: Applet initialized
basic: Removed progress listener: sun.plugin.util.GrayBoxPainter$GrayBoxProgressListener@12611a7
basic: Applet made visible

And that's it. Still haven't figured out why it works with java6 and not java5.

@valli: the object tag was used, not applet

@thorbjorn: i tried that already... it just keeps saying loading applet...

@aaron: how can i know what exception it is, if there really is one? and yes we have considered that its a java bug but i still havent found what that bug is. i have to submit a report tomorrow and i've scoured the net but came up with nothing as of yet...

@all: thank you for your replies