'su nagios' failed for nagios on /dev/?



I am getting this weird message once in a while and when the nagios services come up : ‘su nagios’ failed on /dev/???
The OS is Solaris 10, nagios version is 3.0.6 compiled from sources. There is nothing added to the vanilla example config it is currently running. I’ve trimmed it down to just probing ssh on localhost, so there are no extra plugins which might be causing this.

can someone please suggest which part of nagios might be triggering the above message, and any way I can fix that?