Unable To Create New WorkflowInstance For WorkflowDefinition

I discovered another variant that causes the titular error message.  I was copying the FIM policy config from one data source to another, and that meant making copies of a couple activities within the same workflow.  After some troubleshooting and head-scratching, I realized that FIM was choking on the duplicate activity names (see highlights below).  As you can see, when you build a workflow from the portal, FIM names all activities "authenticationGateActivityX."  And interestingly, if you made the same mistake as I did, and you try to fix it by opening all of the activities within the portal and click "Save," FIM won't fix your mistakes!

<ns0:SequentialWorkflow

  x:Name="SequentialWorkflow"

  ActorId="00000000-0000-0000-0000-000000000000"

  WorkflowDefinitionId="00000000-0000-0000-0000-000000000000"

  RequestId="00000000-0000-0000-0000-000000000000"

  TargetId="00000000-0000-0000-0000-000000000000"

  xmlns:ns1="clr-namespace:IDMware.FIM.Workflow.Activities;Assembly=IDMware.FIM.Workflow, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b6cdb71f2a5e8e65"

  xmlns:ns2="clr-namespace:FimExtensions.FimActivityLibrary;Assembly=FimExtensions.FimActivityLibrary, Version=2.0.0.0, Culture=neutral, PublicKeyToken=68dc29282b77eca9"

  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/workflow"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  xmlns:ns0="clr-namespace:Microsoft.ResourceManagement.Workflow.Activities;Assembly=Microsoft.ResourceManagement, Version=4.1.3559.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">

  <ns1:GenerateRandomPasswordActivity

    x:Name="authenticationGateActivity1"

    DestinationValue="{x:Null}"

    MinPasswordLength="8"

    DestinationString="RandomPassword"

    TheActivityName="Generate random password"

    MaxPasswordLength="10" />

  <ns0:FunctionActivity

    x:Name="authenticationGateActivity6"

    FunctionExpression="<fn id="SingleValueAssignment"  isCustomExpression="false"><arg>[//Target/AccountName]</arg></fn>"

    Description="Grab Target account name"

    Destination="[//WorkflowData/TargetAccountName]" />

  <ns2:PowerShellActivity

    x:Name="authenticationGateActivity5"

    TheActivityName="Powershell: Set AD password"

    PowerShellScript="C:\Scryptography\SetADPwd.ps1" />

  <ns0:FunctionActivity

    x:Name="authenticationGateActivity7"

    FunctionExpression="<fn id="SingleValueAssignment"  isCustomExpression="false"><arg>[//Target/LMSID]</arg></fn>"

    Description="Grab LMS ID"

    Destination="[//WorkflowData/LMSID]" />

  <ns1:ExecuteSQLActivity

    SQLStatement="EXECUTE [dbo].[SetLMSNewUserPassword]    @id   ,@password" x:Name="authenticationGateActivity8"

    SQLConnectionStringName="LMS"

    ParamData="<DocumentElement>   <Parameters>     <ParamName>@id</ParamName>     <ParamValue>[//WorkflowData/LMSID]</ParamValue>     <DataType>Integer</DataType>   </Parameters>   <Parameters>     <ParamName>@password</ParamName>     <ParamValue>[//WorkflowData/RandomPassword]</ParamValue>     <DataType>String</DataType>   </Parameters> </DocumentElement>"

    WorkflowKey="Results"

    TheActivityName="SQL: Set LMS password" />

  <ns0:FunctionActivity

    x:Name="authenticationGateActivity9"

    FunctionExpression="<fn id="SingleValueAssignment"  isCustomExpression="false"><arg>[//Target/VLMID]</arg></fn>"

    Description="Grab VLM ID"

    Destination="[//WorkflowData/VLMID]" />

  <ns1:ExecuteSQLActivity

    SQLStatement="EXECUTE [dbo].[SetVLMNewUserPassword]    @id   ,@password"

    x:Name="authenticationGateActivity10"

    SQLConnectionStringName="VLM"

    ParamData="<DocumentElement>   <Parameters>     <ParamName>@id</ParamName>     <ParamValue>[//WorkflowData/VLMID]</ParamValue>     <DataType>String</DataType>   </Parameters>   <Parameters>     <ParamName>@password</ParamName>     <ParamValue>[//WorkflowData/RandomPassword]</ParamValue>     <DataType>String</DataType>   </Parameters> </DocumentElement>"

    WorkflowKey="VLMResults"

    TheActivityName="SQL: Set VLM password" />

  <ns0:FunctionActivity

    x:Name="authenticationGateActivity9"

    FunctionExpression="<fn id="SingleValueAssignment"  isCustomExpression="false"><arg>[//Target/PDSID]</arg></fn>"

    Description="Grab PDS ID"

    Destination="[//WorkflowData/PDSID]" />

  <ns1:ExecuteSQLActivity

    SQLStatement="EXECUTE [dbo].[SetPDSNewUserPassword]    @id   ,@password"

    x:Name="authenticationGateActivity10"

    SQLConnectionStringName="PDS"

    ParamData="<DocumentElement>   <Parameters>     <ParamName>@id</ParamName>     <ParamValue>[//WorkflowData/PDSID]</ParamValue>     <DataType>String</DataType>   </Parameters>   <Parameters>     <ParamName>@password</ParamName>     <ParamValue>[//WorkflowData/RandomPassword]</ParamValue>     <DataType>String</DataType>   </Parameters> </DocumentElement>"

    WorkflowKey="PDSResults"

    TheActivityName="SQL: Set PDS password" />

  <ns1:ExpressionEvaluator

    x:Name="authenticationGateActivity4"

    DestinationValue="False"

    TheUpdateMode="0"

    Notes=""

    DestinationString="[//Target/SetPassword]"

    ActorID="31415926-5358-9793-2384-626433832795"

    ThisActivityName="Turn off SetPassword flag"

    ValueType="String" />

</ns0:SequentialWorkflow>