Thanks, this worked a treat except there is a typo in your configuration.

The edit should be as follows:

<Extension Name="CSV" Type="Microsoft.ReportingServices.Rendering.CsvRenderer.CsvReport,Microsoft.ReportingServices.CsvRendering">

<Configuration>

<DeviceInfo>

<Encoding>ASCII</Encoding>

</DeviceInfo>

</Configuration>

</Extension>

You have put an extra / ahead of ASCII and before...