[Check_mk (english)] PNP Error: templates/check_mk-netctr.combined.php [52]: Undefined offset: 5

Hi,

When I try to access the performance graphs for network interfaces in
check_mk I get the following error message from PNP4Nagios.

PNP Error
An error was detected which prevented the loading of this page. If
this problem persists, please contact the website administrator.
templates/check_mk-netctr.combined.php [52]:
Undefined offset: 5
Loaded in 0.0276 seconds, using 3.70MB of memory. Generated by Kohana v2.3.4.

Does anybody know something about this kind of error?
Displaying other graphs works fine...

Regards,
Sebastian