Error in workflow in AX 2012

Dear All,

I went to the walkthrough given by microsoft for ax 2012 workflow.

I made Query , workflow category, workflow type … and selected Customer as module.

When i go to accounts receivable> setup> accounts receivable workflows and create a new workflow and select my created workflow type,

I get following error:

An unexpected error has occurred while opening the workflow. See the event log on the AOS and contact your system administrator to resolve the issue

In event viewer:

Workflow threw an exception for the following reason: Class MyWorkflowTypeDocument cannot be instantiated.

Refered to MyWorkflowTypeDocument in classes, its auto-generated code created when I created the workflow type.

Urgent help required…