"W A R N I N G : d2ixjz" in aoforce run - What does it mean and how to avoid it?

[Hauke]

A student I'm supervising gets the following warning in the output of aoforce (using TM Version 6.3.1)

CONSTRUCTING integral bounds

setting up bound for integral derivative estimation

increment for numerical differentiation : 0.00050000
W A R N I N G : d2ixjz =-.845477195605E-07
W A R N I N G : d2ixjz =-.293098357149E-05
W A R N I N G : d2ixjz =-.151166357510E-05
W A R N I N G : d2ixjz =-.321900444260E-05

machine precision:   2.220446049250313E-016

the run continues and the frequencies look reasonable.

Can somebody tell me what this warning is about, if one should be concerned if one gets this warning and what to do to avoid it?

Thanks in advance.