503 for CSV File download

[Alexander Diedler]

Hello,
We have a Typo3 Installation fronted with Varnish 3.0.2 out of the Ubuntu Packages. If we try to load a CSV File, there ist an error:
Error 503 Service Unavailable

Service Unavailable
Guru Meditation:

XID: 1113729206

Varnish cache server

The script create a statistc file, that will be placed in typo3temp.
The header of the file for transfer to the client is :
Pragma: public
Cache-Control: must-revalidate, post-check=0, pre-check=0
Expires: 0
Content-Disposition: attachment; filename= res_GewinnspielDaten_090113-1113.csv
Content-type: x-application/octet-stream
Content-Transfer-Encoding: binary
Content-length:...

Can anybody help us with this issue?

Best regards
AlexD1979