Using multiusers work and queues. working with thethreadsIn an environment
that uses multiple UserWork and Propagation queues, it is possible to generate
a situation where two different Queue threads are compiling the same workflow
expression concurrently. 

When a workflow expression is executed for the first time, 
the codebase\wt\workflow\expr directory is checked for an already compiled 
class file. 

If one is not found the Queue thread creates a .java file, compiles this file 
into the codebase\wt\workflow\expr directory, then removing the .java file. 

The "Bad Workflow Expression" message occurs when two threads concurrently try 
and execute the same workflow expression. The first thread completes 
compilation the .java file there by removing it. However the second thread 
that was depending on the deleted .java file cannot locate it which results 
in the a failed queue entry with the error "Bad Workflow Expression" as the 
message. 

This error should be very rare to the point of almost being non-existent for 
most installations. However regularly deleting the codebase\wt\workflow\expr 
directory will greatly improve the chance of the problem occurring. Deleting 
this directory removes all cached expression class files requiring all 
workflow expressions to be recompiled there by greatly improving the chance 
of the error. 

Setting the wt.workflow.definer.deleteExpressionFiles=false, which will 
maintains all .java files in the $WT_HOME\temp directory.