Install SharePoint 2013 workflow Issue - Unable to load one or more of the requested types, Retrieve the LoaderExceptions property for more information.

To be able to use SharePoint workflow 2013, I have configured workflow manager 1.0 successfully.
as http://www.aboutworkflows.com/2012/07/sharepoint-2013-install-sharepoint-2013.html

Then run this command in SharePoint PowerShell,
Register-SPWorkflowService -SPSite http://SERVERNAME -WorkflowHostUri http://SERVERNAME:12291 -AllowOAuthHttp

I got the following error,
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:/ ...

The reason is because of the SharePoint Developer Tools for visual studio 2012 preview is also installed.

- Uninstall the sharepoint developer tools for visual studio 2012 preview
- Restart Server
- Run the powershell command again then it worked.
- Also a new office developer tools for visual studio 2012 preview 2 has been released, so I just installed that from web platform installer.