unable to open customised workflow( unexpected error has occured)

I have created workflow for RFQ , place its menu item in procurement and sourcing , when i open my workflow for designing purpose ....m geting error as :

An unexpected error has occurred while opening the workflow. See the event log on the AOS and contact your system administrator to resolve the issue.

in my windows event viewer I am encountered with messages as:

Workflow threw an exception for the following reason: The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state. %2

ny1 knows about this issue ??

thanks