Redmine

I have problem with update issue, who can help me?

and my Environment:

Redmine version 2.0.3.stable
Ruby version 1.9.3 (x86_64-linux)
Rails version 3.2.6
Environment production
Database adapter PostgreSQL
Redmine plugins:
redmine_importer 1.0 for redmine 2.x
redmine_screenshot_paste 2.1.0
redmine_work_time 0.2.6
redmine_xls_export 0.2.1

I have bug when i update issue, can you help me ? please .....please.....
and link
https://github.com/ksauzz/redmine_importer/tree/redmine2.x

NoMethodError (undefined method strftime' for nil:NilClass):
app/models/mailer.rb:459:inmessage_id_for'
app/models/mailer.rb:413:in mail'
app/models/mailer.rb:413:incollect'
app/models/mailer.rb:413:in mail'
app/models/mailer.rb:76:inissue_edit'
app/models/mailer.rb:427:in initialize'
app/models/mailer.rb:440:inmethod_missing'
app/models/journal_observer.rb:26:in after_create'
app/models/journal.rb:52:insave'
app/models/issue.rb:1362:in `create_journal'

Thanks admin so much
my boss deadline for me 7 day,
pls help help help