Can't generate spreadsheet

When I try to generate a spreadsheet from a availability page I get the followind error:

Could not generate report.
Check that the /home/xymon/server/www/rep/ directory has permissions '-rwxrwxr-x' (775)
and that is is set to group 8 
Permissions and group ownership are as requested. Generating the same report
as HTML report works - it is written into the above mentioned directory.

Xymon version is  4.3.0-0.beta2 and operating system openSuSE 11.1.

Any hints?
hjb