SharePoint 2013 Workflow Manager error when I register workflow service

When I try to register the workflow service according to http://technet.microsoft.com/en-us/library/jj658588%28v=office.15%29 by the folloing command: Register-SPWorkflowService –SPSite "http://mysharepointserver" –WorkflowHostUri "http://localhost:12291" –AllowOAuthHttp

I got this error:

Register-SPWorkflowService : Unable to load one or more of the requested types.
 Retrieve the LoaderExceptions property for more information.
At line:1 char:1
+ Register-SPWorkflowService –SPSite "http://mysharepointserver" –WorkflowHostUri "h
ttp:/ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~
    + CategoryInfo          : InvalidData: (Microsoft.Share...WorkflowService:
   RegisterSPWorkflowService) [Register-SPWorkflowService], ReflectionTypeLoa
  dException
    + FullyQualifiedErrorId : Microsoft.SharePoint.WorkflowServices.PowerShell
   .RegisterSPWorkflowService

Is there any idea?