Resolution:
This problem may be related to a Sun bug reported in the following link:
    http://bugs.sun.com/bugdatabase/view_bug.do;jsessionid=bae468a1f0ffb3ffffffffc059692d1942ecb:WuuT?bug_id=6215380

We have located 2 links of potential workaround:
    http://forum.java.sun.com/thread.jspa?threadID=722656

<<<
One work around is to turn off the hot spot compiler, my error went away after that.
Use
-Djava.compiler=NONE
on the java command line
>>>

You can start TIBCO Designer with the following JVM option...  
    -Djava.compiler=NONE

Or you can add the below line to designer.tra:
    java.extended.properties -Djava.compiler=NONE

Adding "java.extended.properties -Djava.compiler=NONE" to the designer.tra file
would prevent Designer from crashing.

However, it takes a long time to load the first project.

Another link with info and workaround:
    http://www-128.ibm.com/developerworks/forums/dw_thread.jsp?message=13808462&cat=10&thread=114275&treeDisplayType=threadmode1&forum=843#13808462

Which suggests the following:
<<&ltThe other possibility is to drop back to an older JVM on the client, since the
problem is probably specific to 1.5.0.>>>