The parameter mxhko defines the maximum order for the Taylor
expansion implicit in the Hautman-Klein Ewald method. DL_POLY_2 has a maximum
of mxhko = 3, but it can be set to less in some
implementations. If this error arises when the user requestes an
order in excess of this parameter.
Action:
Standard user response. Set the parameter mxhko
to a higher value (if it is 
3) and recompile the
program. Alternatively request a lower order in the CONTROL file
through the nhko variable (see 4.1.1).