At the moment it is not possible to query the process variables in the tasklist if a variable is of an application provided complext type.

The result is a class not found exception (see this thread: https://groups.google.com/forum/?fromgroups#!topic/camunda-bpm-users/3n8zkeg07tI).

Solution:
Fix problem (i.e. use the execute-in-context-of-webapplication-classpath mechanism provided by the platform) or ignore the process variables that cannot be deserialized.