Set document approval status within approval workflow

Hi

I have a Document Library with the following Settings: -

Require content approval for submitted items=  Yes
Require documents to be checked out before they can be edited=No

I have a SPD approval workflow acting on a document library.  Everything works but I am now required that the user is forced to check-out the document.

I now set the document library to :

Require content approval for submitted items=  Yes
Require documents to be checked out before they can be edited=Yes

The workflow fails due to requiring the document to be checked-out. So I add the following actions within the workflow

'Checkout item in current item' and 'Set Content Approval status to Approved' Actions in the workflow

Now workflow checks out document, but a different error occurs. workflow history shows :User Id System Account, Event type - Error

The workflow could not update the item, possibly because one or more columns for the item require a different type of information.

I've looked for soltions but cant find any answers. Any help appreciated, using 2010 with latest CU.

I've added actions to 'When a Task Completes'

System.Workflow.Runtime.Hosting.PersistenceException: You cannot perform this action on a checked out document. ---> Microsoft.SharePoint.SPException: You cannot perform this action on a checked out document.    
 at Microsoft.SharePoint.SPListItem.SetRequiredInfoForUpdateItem(Boolean bDocLib, Boolean bAdd, Boolean bMigrate)    
 at Microsoft.SharePoint.SPListItem.PrepareItemForUpdate(SPWeb web, Boolean bMigration, Boolean& bAdd, Boolean& bPublish, Object& objAttachmentNames, Object& objAttachmentContents, Int32& parentFolderId)    
 at Microsoft.SharePoint.SPListItem.UpdateInternal(Boolean bSystem, Boolean bPreserveItemVersion, Guid newGuidOnAdd, Boolean bMigration, Boolean bPublish, Boolean bNoVersion, Boolean bCheckOut, Boolean bCheckin, Boolean suppressAfterEvents, String filename, Boolean bPreserveItemUIVersion)    
 at Microsoft.SharePoint.SPListItem.Update()    
 at Microsoft.SharePoint.Workflow.SPWinOEWSSService.CommitUpdateDocument(Transaction txn, Object[] transData)    
 at Microsoft.SharePoint.Workflow.SPPendingWorkBatch.Commit(Transaction transaction, ICollection items)    
 at System.Workflow.Runtime.WorkBatch.PendingWorkCollection.Commit(Transaction transaction)    
 at System.Workflow.Runtime.WorkBatch.Commit(Transaction transaction)    
 at System.Workflow.Runtime.Hosting.WorkflowCommitWorkBatchService.CommitWorkBatch(CommitWorkBatchCallback commitWorkBatchCallback)    
 at System.Workflow.Runtime.Hosting.DefaultWorkflowCommitWorkBatchService.CommitWorkBatch(CommitWorkBatchCallback commitWorkBatchCallback)    
 at System.Workflow.Runtime.WorkflowExecutor.CommitTransaction(Activity activityContext)    
 at System.Workflow.Runtime.WorkflowExecutor.Persist(Activity dynamicActivity, Boolean unlock, Boolean needsCompensation)     -
 -- End of inner exception stack trace ---    
 at System.Workflow.Runtime.WorkflowExecutor.Persist(Activity dynamicActivity, Boolean unlock, Boolean needsCompensation)    
 at System.Workflow.Runtime.WorkflowExecutor.System.Workflow.ComponentModel.IWorkflowCoreRuntime.PersistInstanceState(Activity activity)    
 at System.Workflow.ComponentModel.Activity.MarkClosed()    
 at System.Workflow.ComponentModel.Activity.ReleaseLockOnStatusChange(IActivityEventListener`1 eventListener)    
 at System.Workflow.ComponentModel.FaultAndCancellationHandlingFilter.SafeReleaseLockOnStatusChange(ActivityExecutionContext context)    
 at System.Workflow.ComponentModel.FaultAndCancellationHandlingFilter.OnEvent(Object sender, ActivityExecutionStatusChangedEventArgs e)    
 at System.Workflow.ComponentModel.ActivityExecutorDelegateInfo`1.ActivityExecutorDelegateOperation.Run(IWorkflowCoreRuntime workflowCoreRuntime)    
 at System.Workflow.Runtime.Scheduler.Run()