[ns] please help if you can " wimax HO "

am working in wimax model
when am increasing the mobile node to more then 5 node i get this error
anyone know how to fix this please help me out

Configuration of hierarchical addressing done
num_nodes is set 9
sink node created
INITIALIZE THE LIST xListHead
warning: no class variable WimaxScheduler/BS::use_pmip6_ext_

    see tcl-object.tcl in tclcl for info about this warning.

Base Station 1 created
warning: no class variable WimaxScheduler/BS::use_pmip6_ext_

    see tcl-object.tcl in tclcl for info about this warning.

Base Station 2 created
wireless nodes created ...

Running simulation
channel.cc:sendUp - Calc highestAntennaZ_ and distCST_
highestAntennaZ_ = 1.5,  distCST_ = 83.4
SORTING LISTS ...DONE!
Scheduler: Event UID not valid!