Zoho return error code 3838 ? Who can help me?

I used Zoho show: http://show.zoho.com for edit/view remote document

"http://show.zoho.com/remotedoc.im?output=view&apikey=<Api Key>"

AND POST SOME PARAM:
[cookiejar:protected] =>
[last_request:protected] => POST /remotedoc.im?output=view&apikey=<MyAPIkey>
&url=<MyURL>
&saveurl=<MySavedURL>
&filename=Robstertestold.ppt&id=545&format=ppt&persistence=true
HTTP/1.1
Host: show.zoho.com
Connection: close
Accept-encoding: gzip, deflate
Content-type: application/x-www-form-urlencoded
User-agent: Zend_Http_Client

And i use the same function to prepare zoho.(check for edit/view in zoho).
With doc,xls,... it wokrs ok.

But observed:

With ppt file extention, Zoho return error code 3838 (Invalid file extension for {0}).
Why it's return it?

Notes that: i use the same function to prepare zoho(request to zoho to check file doc,xls,ppt...).