Cisco ASDM is quirky in the sense that if the right Java version is not found it will just puke with errors that make no sense. This is what my java log looks like:
Application Logging Started at Fri Aug 01 11:01:11 EDT 2010
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Local Launcher Version = 1.5.41
Local Launcher Version Display = 1.5(41)
Cannot read profile file C:\Documents and Settings\abcdef\.asdm\data\deviceinfo.conf.
OK button clicked
Trying for ASDM Version file; url = https://www.example.com/admin/
Server Version = 6.2(1)
Server Launcher Version = 1.5.41, size = 476672 bytes
Launcher version checking is successful.
invoking SGZ Loader..
Cache location = C:/Documents and Settings/abcdef/.asdm/cache
Exception in thread "SGZ Loader: launchSgzApplet" java.lang.NoSuchFieldError: b
at dac.setLevel(dac.java:65)
at dac.(dac.java:44)
at gd.(gd.java:78)
at f5.a(f5.java:117)
at com.cisco.dmcommon.util.DMCommonEnv.(DMCommonEnv.java:38)
at com.cisco.pdm.PDMApplet.updateProgress(PDMApplet.java:300)
at com.cisco.pdm.PDMApplet.init(PDMApplet.java:63)
at com.cisco.nm.dice.loader.r.run(DashoA19*..:409)

It happens because the ASDM launcher is not capable of running on newer JVMs. Since I had older JVMs, I went into Control Panel -> Java. Click on the Java tab, followed by clicking the “view” button. This will show you the current JVM being used. If you have older JVMs click on Find (you will have to select the folder where you suspect older JVMs to be…which in my case was c:\Program Files). If you don’t find an older JVM then just install an older version and it will work.