SPD Workflow Custom Action - Cannot create unknown type

Question

I have written a custom workflow activity in Visual Studio 2012. I have deployed the dll and allowedtypes.xml etc etc and it is showing up when I look in Sharepoint Designer to add an action. I can add it to the workflow and interact with it just fine, setting the variables, but when I go to publish any workflow with that action in it, I get the error below. I do not know what to be looking for from here. How can I proceed, or what should I try looking for?

Microsoft.Workflow.Client.ActivityValidationException: Workflow XAML failed validation due to the following errors:
Cannot create unknown type '{clr-namespace:testCustomWorkflowAction;assembly=testCustomWorkflowAction}testActionCode'. HTTP headers received from the server - ActivityId: fa97008a-ebd8-4953-b285-4518eed5853f. NodeId: XXXX-XXXXXXXX. Scope: /SharePoint/default/d83c404d-b1b9-4e4c-ba22-72000556ca18/5acdea96-83f7-4403-8b0a-a4b8824e15ff. Client ActivityId : b41f169d-cdeb-50dc-3698-00c71

My actions4 file:

<?xml version="1.0" encoding="utf-8"?>
<WorkflowInfo Language="en-us">
  <Actions>
    <Action Name="TestAddUsertoGroup"
      ClassName="testCustomWorkflowAction.testActionCode"
      Assembly="testCustomWorkflowAction, Version=1.0.0.0, Culture=neutral, PublicKeyToken=106c0bc3254af6c0"
      AppliesTo="all"
      Category="Core Actions">
      <RuleDesigner Sentence="Adds user: %1 to group: %3 on site: %2">
        <FieldBind Field="User" Text="User ID" Id="1" DesignerType="Integer" DisplayName="UserID" />
        <FieldBind Field="Site" Text="Site URL" Id="2" DesignerType="StringBuilder" DisplayName="SiteURL" />
        <FieldBind Field="Group" Text="Group Name" Id="3" DesignerType="StringBuilder" DisplayName="GroupName" />
      </RuleDesigner>
      <Parameters>
        <Parameter Name="User" Type="System.Int32, mscorlib" Direction="In" DesignerType="Integer"
            Description="Param var" />
        <Parameter Name="Site" Type="System.String, mscorlib" Direction="In" DesignerType="StringBuilder"
            Description="Param var" />
        <Parameter Name="Group" Type="System.String, mscorlib" Direction="In" DesignerType="StringBuilder"
            Description="Param var" />
      </Parameters>
    </Action>
  </Actions>
</WorkflowInfo>

My AllowedTypes.xml file:

<?xml version="1.0" encoding="utf-8" ?>
<AllowedTypes>
  <Assembly Name="testCustomWorkflowAction, Version=1.0.0.0, Culture=neutral, PublicKeyToken=106c0bc3254af6c0">
    <Namespace Name="testCustomWorkflowAction">
      <Type>testCustomWorkflowAction</Type>
    </Namespace>
  </Assembly>
</AllowedTypes>

My CS file:

[BuildActivity(HostEnvironmentOption.All)]  
class testActionCode : CodeActivity
{
    // Define an activity input argument of type string
    [RequiredArgument]
    public InArgument<int> User { get; set; }//%1
    [RequiredArgument]
    public InArgument<string> Site { get; set; }//%2
    [RequiredArgument]
    public InArgument<string> Group { get; set; }//%2

    protected override void Execute(CodeActivityContext context)
    {
        // Obtain the runtime value of the Text input argument
        int user = context.GetValue(this.User);
        string siteUrl = context.GetValue(this.Site);
        string group = context.GetValue(this.Group);

        try
        {

            using (SPSite site = new SPSite(siteUrl))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    SPGroup mySpGroup;
                    web.AllowUnsafeUpdates = true;
                    mySpGroup = web.SiteGroups[group];
                    SPUser mySPUSER = web.AllUsers.GetByID(user);
                    mySpGroup.AddUser(mySPUSER);
                    mySpGroup.Update();
                    web.Update();
                }
            }
        }
        catch (Exception ex)
        {
        }
    }
}

Answer 1

I strongly recommend you to double-check the assembly full name (including version and public key token), and check whether it is well-deployed in the GAC of every server in the farm.