error updating existing issues

[RkWaters]

I love your plug-in!!!
Importing new issues works great!!

When I try to update any existing issues, I get the error message and log entry below.

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Internal error

An error occurred on the page you were trying to access.
If you continue to experience problems please contact your Redmine administrator for assistance.

If you are the Redmine administrator, check your log files for details about the error.

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Processing ImporterController#result (for [=my PC's IP addr=] at 2013-01-30 13:33:54) [POST]
Parameters: {"commit"=>"Submit", "fields_map"=>{"Start date"=>"start_date", "Subject"=>"", "#"=>"", "ID number"=>""}, "ignore_non_exist"=>"true", "project_id"=>"22", "unique_field"=>"ID number", "action"=>"result", "authenticity_token"=>"OzqiZv...blah...rPZcIBBaK4=", "update_issue"=>"true", "controller"=>"importer", "import_timestamp"=>"2013-01-30 13:31:51", "default_tracker"=>"8", "journal_field"=>"#", "update_other_project"=>"true"}

ArgumentError (interning empty string):
vendor/plugins/redmine_importer/app/controllers/importer_controller.rb:262:in to_sym' vendor/plugins/redmine_importer/app/controllers/importer_controller.rb:262:inresult'
lib/faster_csv.rb:1521:in each' vendor/plugins/redmine_importer/app/controllers/importer_controller.rb:224:inresult'
config/initializers/mongrel_cluster_with_rails_211_fix.rb:62:in `dispatch_cgi'

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I think I'm using the latest plug-in version:

Issue Importer Issue import plugin for Redmine.
Martin Liu / Leo Hourvitz 1.0 c65c222....

The plugin folder is named 'redmine_importer'.

I followed the directions in the Wiki and Sample file - https://github.com/leovitch/redmine_importer/wiki

Using: Redmine 1.2.1.stable (MySQL)

Please help!!

Rick