Nfsiostat rrd graph error

I’ve started using the nfsiostat agent plugin on some servers where I want to know more about the servers’ NFS-client activity.

And when looking in Checkmk’s web-interface, I do see NFS stats numbers in a new monitoring item. However, the related RRDtool graphs are broken, see attached screenshot.

I have not succeeded finding anything interesting in log files on the server where Checkmk’s server-part is installed.

How do I troubleshoot further?

The error has been seen with the following server/agent version combinations:
Server: 1.6.0p14, agent: 1.6.0p9.
Server: 1.6.0p8, agent: 1.6.0p9.
Server: 1.6.0p7, agent: 1.6.0p13.

Troels Arvin