Instead of using root explorer I used the following commands in android sdk environment

Copied the DroidSansFallback.ttf file into root of sdcard and issued the following commands

adb shell
su
mount -o remount,rw -t yaffs2 /dev/block/mtdblock3 /system
cd /sdcard
busybox cp DroidSansFallback.ttf /system/fonts
mount -o ro,remount -t yaffs2 /dev/block/mtdblock3 /system
exit
exit

Rebooted the phone