Delayed job cannot process email

Hi all.
I'm using DelayedMailhopper (with MailHopper and Delayed Jobs). When I send my email, I get it to Email table and the task to be executed to DelayedJobs table. But when DelayedJobs daemon tries to execute this task, I get this error:

BEGIN
Delayed::Backend::ActiveRecord::Job Load (0.5ms) SELECT "delayed_jobs".* FROM "delayed_jobs" WHERE "delayed_jobs"."id" = $1 LIMIT 1 FOR UPDATE ["id", 1218] UPDATE "delayed_jobs" SET "locked_at" = '2013-04-11 10:02:24.582308', "locked_by" = 'host:anahorets-iMac-4.local pid:17549', "updated_at" = '2013-04-11 10:02:24.586329' WHERE "delayed_jobs"."id" = 1218
(0.5ms) COMMIT
(0.4ms) BEGIN
(0.7ms) UPDATE "delayed_jobs" SET "last_error" = 'Job failed to load: invalid subclass. Handler: "--- !ruby/struct:DelayedMailhopper::SendJob \nid: 1212\n"
/usr/local/opt/rbenv/versions/1.9.3-p374/lib/ruby/gems/1.9.1/gems/delayed_job-3.0.5/lib/delayed/backend/base.rb:87:in rescue in payload_object'' /usr/local/opt/rbenv/versions/1.9.3-p374/lib/ruby/gems/1.9.1/gems/delayed_job-3.0.5/lib/delayed/backend/base.rb:85:inpayload_object''
/usr/local/opt/rbenv/versions/1.9.3-p374/lib/ruby/gems/1.9.1/gems/delayed_job-3.0.5/lib/delayed/backend/base.rb:95:in block in invoke_job'' /usr/local/opt/rbenv/versions/1.9.3-p374/lib/ruby/gems/1.9.1/gems/delayed_job-3.0.5/lib/delayed/lifecycle.rb:60:incall''
/usr/local/opt/rbenv/versions/1.9.3-p374/lib/ruby/gems/1.9.1/gems/delayed_job-

I think the problem is here:

delayed_jobs" SET "last_error" = 'Job failed to load: invalid subclass. Handler: "--- !ruby/struct:DelayedMailhopper::SendJob \nid: 1212\n

But I dont know how to resolve it.