How is he running the workflow?  Maybe this is a 2013 thing, but you can't manually start a workflow on a checked out document.  

Hi Brendan,

Thanks for your reply.

He is running the approval workflow using the task form. User has option to approve and reject the document in the task form.

Could you elaborate on the process?  When you say they can approve/reject the document in a task form, this implies and approval task which would require a workflow to already be running.  Approving/rejecting a task doesn't start another workflow, unless you have a second workflow.  How does this process start?  When does the workflow start?  What are the triggers?  Can you give a screen shot of the workflow?  

Hi Brendan,

The process is below -

1. Author uploads a documents and starts a Review workflow by selecting a reviewer for that particular category of document.

2. Reviewer is notified via email and also he gets a task created in his My workflow tasks.

3. He clicks the document link from his workflow tasks and edits it.

4. Then without saving or check in the document (step 3), he approves the document using link from his workflow task.

5. This triggers the error "Workflow failed as the document is checked out".

Hope I am able to clarify. Let me know if you need more details.

Appreciate your help in resolving this.

Thanks.

Yes, that helps.  Now I understand.  So the workflow is in progress and someone checks out the document, but doesn't check it back in.  The workflow continues and gets to a step where it needs to update the document, but can't because the user has it locked, so it errors out.

I don't think you can get the workflow to check-in the document, since someone else has it checked out.  I have not tried this though.  However, how I handle this situation is by putting a check in place in the workflow before I attempt to update the document, to validate that it is checked in and can be updated.  

1. Add a Run If action that looks to see if the Checked Out field is populated.  
2. Within the Run If, I add a Send Notification action that goes to the person in the Checked-Out field with a link to the document advising them they need to check the document in so the workflow can continue.
3. Then I add a Wait for check out status to change action.  This pauses the workflow until the document is checked-in.  Once the document is checked-in, then it will continue.

Thanks for your reply Brendan.

I will implement this and let you know the results.

Thanks again.