Hi Abhishek, I tried nesting (by dragging) the 1280x720 sequence with the warp stabilizer into the master sequence (1920x1080) and it still states that the settings do not match and whether I want to change the sequence settings.
Nesting stabilized 1280x720 sequence in a 1920x1080 is working fine.
Create a sequence of 1280x720 clip using "New sequence from clip".
apply warp stabilizer to the clip.
drag the sequence from the project panel to 1920x1080 sequence. you can right click on the sequence and select "scale to frame size" to fill the frame completely.
You're probably better off working in 720 sequence entirely, scaling your 1080 footage down instead of upresing the 720 clips.
This has the added benefit of solving this issue.