• I resolved this by using the DeviceInfo FileExtension tags and also adding an ExtensionName for the TTX file output

    <Render>

    <Extension Name="XML" Type="Microsoft.ReportingServices.Rendering.DataRenderer.XmlDataReport,Microsoft.ReportingServices.DataRendering"/>

    <Extension Name="NULL" Type="Microsoft.ReportingServices.Rendering.NullRenderer.NullReport,Microsoft.ReportingServices.NullRendering" Visible="false"/>

    <Extension Name="TTX" Type="Microsoft.ReportingServices.Rendering.DataRenderer.CsvReport,Microsoft.ReportingServices.DataRendering">

    <OverrideNames>

    <Name Language="en-US">TTX for EDI</Name>

    </OverrideNames>

    <Configuration>

    <DeviceInfo>

    <FileExtension>TTX</FileExtension>

    </DeviceInfo>

    </Configuration>

    </Extension>

    <Extension Name="CSV" Type="Microsoft.ReportingServices.Rendering.DataRenderer.CsvReport,Microsoft.ReportingServices.DataRendering"/>

    <Extension Name="TTX" Type="Microsoft.ReportingServices.Rendering.DataRenderer.CsvReport,Microsoft.ReportingServices.DataRendering"/>

    <Extension Name="ATOM" Type="Microsoft.ReportingServices.Rendering.DataRenderer.AtomDataReport,Microsoft.ReportingServices.DataRendering" Visible="false"/>

    <Extension Name="PDF" Type="Microsoft.ReportingServices.Rendering.ImageRenderer.PDFRenderer,Microsoft.ReportingServices.ImageRendering"/>

    <Extension Name="RGDI" Type="Microsoft.ReportingServices.Rendering.ImageRenderer.RGDIRenderer,Microsoft.ReportingServices.ImageRendering" Visible="false"/>

    <Extension Name="HTML4.0" Type="Microsoft.ReportingServices.Rendering.HtmlRenderer.Html40RenderingExtension,Microsoft.ReportingServices.HtmlRendering" Visible="false"/>

    <Extension Name="MHTML" Type="Microsoft.ReportingServices.Rendering.HtmlRenderer.MHtmlRenderingExtension,Microsoft.ReportingServices.HtmlRendering"/>

    <Extension Name="EXCEL" Type="Microsoft.ReportingServices.Rendering.ExcelRenderer.ExcelRenderer,Microsoft.ReportingServices.ExcelRendering"/>

    <Extension Name="RPL" Type="Microsoft.ReportingServices.Rendering.RPLRendering.RPLRenderer,Microsoft.ReportingServices.RPLRendering" Visible="false" LogAllExecutionRequests="false"/>

    <Extension Name="IMAGE" Type="Microsoft.ReportingServices.Rendering.ImageRenderer.ImageRenderer,Microsoft.ReportingServices.ImageRendering"/>

    <Extension Name="WORD" Type="Microsoft.ReportingServices.Rendering.WordRenderer.WordDocumentRenderer,Microsoft.ReportingServices.WordRendering"/>

    </Render>