I wonder are you and your colleagues use the same environments and if yes are your and his user have the same permissions and user roles ?
About the second question I saw you are using Sitefinity 6.3 what you can do is to start Workflow as InProcess instead of as WCF service.
You can read the 6.3 release notes here http://www.sitefinity.com/developer-network/forums/general-discussions-/sitefinity-6-3-released and this feature can be ENABLED by unchecking a checkbox in Sitefinity >> Settings >> Advanced >> Workflow >> Run workflow as WCF Service ( see attached screenshot)
I hope I was able to help you.
Please do not hesitate to contact me if you need more help.
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