Workflow ‘InvalidCastException’ or ‘Workflow contains an invalid custom activity’ Error | Oracle Series

Issue

Sometimes on importing a solution in CRM v8.x, it might fail with the error: ‘Workflow contains an invalid custom activity’. In an effort to try to conquer the ambiguity, I tried to create said Workflow manually on the target environment.

Adding each step went well until I noticed that one of those steps, namely a certain Custom Step, caused the error: ‘InvalidCastException’. The error might look something like this:

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=8.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: System.InvalidCastException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #B947377DDetail: 
<OrganizationServiceFault xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/xrm/2011/Contracts">
  <ActivityId>b1989af8-b3e2-4e77-b8bc-6630796f0063</ActivityId>
  <ErrorCode>-2147220970</ErrorCode>
  <ErrorDetails xmlns:d2p1="http://schemas.datacontract.org/2004/07/System.Collections.Generic" />
  <Message>System.InvalidCastException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #B947377D</Message>
  <Timestamp>2020-06-25T09:13:07.4937933Z</Timestamp>
  <ExceptionRetriable>false</ExceptionRetriable>
  <ExceptionSource i:nil="true" />
  <InnerFault i:nil="true" />
  <OriginalException i:nil="true" />
  <TraceText i:nil="true" />
</OrganizationServiceFault>

Investigation

Upon further investigation, it turned out that the Custom Step accepts an Option-set argument with a default value set.

The following code highlights the issue:

        [Input("Option-set Field")]
        [AttributeTarget("new_test", "new_optionsetfieldcode")]
        [Default("1")]
        public InArgument<OptionSetValue> OptionSetFieldArg { get; set; }

On line 3, the Default Attribute caused an error because of the String value. It seems that CRM tries to cast it to an Integer but fails.

Solution

Removing said Attribute fixed the issue.

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