EREngine-config.xml located at Elixir Repertoire\config controls the availability of renderer such as xls, ppt etc as listed above.

For example,

<!--render name="application/vnd.ms-excel" class="com.elixirtech.
  report2.engine.XLSPipeline"/-->

indicates the xls renderer has been disabled. In other words, the xls renderer had been mask off. To enable the renderer, simply remove the comment, as shown below.

<render name="application/vnd.ms-excel" class="com.elixirtech.
  report2.engine.XLSPipeline"/>