unable to create IOpowr padring using Sroute in SOCEncounter

Hi
For our ASIC, we have a set of core power pads that supply 1.8v to core area and another set of IO power pads that supply 3.3vto IO pads.

We are able to do successful Sroute to connect std_cells VCC& GND to core power/ground nets and to the COre power pad pins.

However, when I do sroute for creating pad ring, I get the following error
"**WARN: (SOCSR-1255): Net power does not have pad pins to create pad
ring. Please check net list or port class. (must NOT be CORE class and
must not be AREAIO subclass).

here is the snippet of io.lef for IO power pad
MACRO VCC3IOD
CLASS PAD ;
FOREIGN VCC3IOD 0.000 0.000 ;
ORIGIN 0.000 0.000 ;
SIZE 62.620 BY 140.120 ;
SYMMETRY x y r90 ;
SITE iocore_d ;
PIN VCC3O
DIRECTION INOUT ;
USE ANALOG ;
PORT
LAYER metal6 ;
RECT 2.850 0.000 59.770 3.000 ;
LAYER metal5 ;
RECT 2.850 0.000 59.770 3.000 ;
LAYER metal4 ;
RECT 2.850 0.000 59.770 3.000 ;
LAYER metal3 ;
RECT 2.850 0.000 59.770 3.000 ;
LAYER metal2 ;
RECT 2.850 0.000 59.770 3.000 ;
LAYER metal1 ;
RECT 2.850 0.000 59.770 3.000 ;
END
END VCC3O

Can anybody please tell me what could be wrong?
Do I need to specify different power/ground nets for IO pad ring? Do I need to modify .lef file? DO i need to associate pad pins to IO power/ground nets in GlobalConnect?
I've tried but still it fails.

Thanks