Exporting in XLS does not work in external access

Hello,

I'm facing a problem on a 7.2 installation where I don't find a solution. I cannot export in XLS when using the CRM externaly (https).

-> Internaly ( localhost or name of the server), I can export in XLS, I can see my dashboard and the spellcheck works as expected. -> tomcat and redirector seem to work. The exchange synch uses also Tomcat.

-> Externally, interactive dashboard and spellcheck are working but I cannot export in XLS.

I got this message:

"An Error occurred while running the report"

The logs say it is a 404:

START - doEndpointPost URL: Externaladdress/.../spreadsheetTask
jan 6 2015 17:06:59.765 4508 404 1 CRMOpenThreadTokenWinVista
jan 6 2015 17:06:59.781 4508 404 5 FINISHED - doEndpointPost time-taken: 16ms. HTTP status code: 404

ERROR generating excel file. HTTP status:404 Message: <?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"">www.w3.org/.../xhtml1-transitional.dtd">
<html xmlns="">http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>404 - Not Found</title>
</head>
<body>
<h1>404 - Not Found</h1>
</body>
</html>

jan 6 2015 17:07:00.203 4508 404 1 ERROR generating excel file. Message - Error generating report. .

Does anyone have an idea to resolve this?

Do we have a parameter only for reports?

Thanks for your help

Jerome