CRM 2011 Plugin showing up error when it is called from a normal workflow .

Hi  all,

I'm facing an issue with custom autonumber plugin when it is called from a normal CRM workflow . it is running independently while creating a record in CRM 2011 .

Error Message :

Plugin Trace:
[Microsoft.Xrm.Sdk.Workflow: Microsoft.Xrm.Sdk.Workflow.Activities.CreateEntity]
[CreateStep17: Create test ]

[AutoNumber: AutoNumber]
[e6b77ab3-bbce-e211-8641-4a9c2a321208: AutoNumber: Create of test]


[Microsoft.Crm.ObjectModel: Microsoft.Crm.ObjectModel.TargetAttributeValidationPlugin]
[fc743e7d-fbea-4695-bdb9-7d78334c8474: TargetAttributeValidationPlugin]





Error Message:

Unhandled Exception: Microsoft.Xrm.Sdk.InvalidPluginExecutionException: An error occurred in the plug-in.

Could any one please help me to resolve this issue ? Also I am not able to debug this plugin when calling via normal workflow .

Thanks

Sandy