Exception thrown from GH listener when running Jelly scripts

There's an exception from GreenHopper whenever I run a jelly script that performs a workflow transition an an issue (call it SOURCE-1). This transition triggers the "copy-and-link" function of a custom plugin (created by another company):

• a new issue is created on another project, for example TARGET-1 (this new issue is also properly indexed)
• the new issue TARGET-1 is linked to the source issue SOURCE-1

This "copy-and-link" functionality works fine, but there are exceptions from GreenHopper in the jira log messages. The relevant messages are below. I have posted the detailed log here:
http://pastebin.com/f1a5f707e

Does anyone know what causes these exceptions?
I have already tried removing GreenHopper's "ranking" custom field, but the error messages still appear.

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2009-02-20 13:27:27,366 TP-Processor5 ERROR [jira.event.issue.IssueEventDispatcher] Exception thrown from listener [com.pyxis.greenhopper.jira.customfields.GreenHopperCTFIndexer] : null
java.lang.NullPointerException
at webwork.action.factory.ApplicationMap.get(ApplicationMap.java:131)
at com.pyxis.greenhopper.jira.configurations.GeneralConfiguration.load(GeneralConfiguration.java:155)
at com.pyxis.greenhopper.jira.configurations.GHConfiguration.<init>(GHConfiguration.java:42)
at com.pyxis.greenhopper.jira.customfields.GreenHopperCTFIndexer.issueCreated(GreenHopperCTFIndexer.java:50)
at com.atlassian.jira.event.issue.AbstractIssueEventListener.workflowEvent(AbstractIssueEventListener.java:110)
at com.atlassian.jira.event.issue.IssueEventDispatcher.dispatchEvent(IssueEventDispatcher.java:125)
at com.atlassian.jira.event.issue.IssueEventDispatcher.dispatchEvent(IssueEventDispatcher.java:89)
at com.atlassian.jira.workflow.function.event.FireIssueEventFunction.execute(FireIssueEventFunction.java:60)
at com.opensymphony.workflow.AbstractWorkflow.executeFunction(AbstractWorkflow.java:869)
at com.opensymphony.workflow.AbstractWorkflow.transitionWorkflow(AbstractWorkflow.java:1265)
at com.opensymphony.workflow.AbstractWorkflow.initialize(AbstractWorkflow.java:61
at com.atlassian.jira.workflow.SimpleWorkflowManager.createIssue(SimpleWorkflowManager.java:217)
at com.atlassian.jira.issue.managers.DefaultIssueManager.createIssue(DefaultIssueManager.java:337)
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