postgis - geodjango application in rhel 6 -

postgis - geodjango application in rhel 6 -

i have developed geodjango application using python 2.7, django 1.4, mapnik, tilecache , postgis enabled postgresql in ubuntu 12.04. after completing development installed same application in rhel 6, postgis query using geodjango api not working. query is

the_geom geometry value table

placedet = mymodel.objects.filter(thegeom__dwithin=(the_geom, 250)).distance(the_geom).order_by('distance')

and in exception shows error as,

'nonetype' object has no attribute 'group'

please help me solve issue!

postgis geodjango rhel6