I was able to fix the issue by creating a new world and pasting again, this time aligning chunks. It appears the partial chunks were the cause of the crashing.
No. The world was 1.7.4 generated. The same issue appeared when trying to use 1.7.2 as well. There is this strange gap between the pasted area and neighboring chunks, could that be an issue?
I was able to fix the issue by creating a new world and pasting again, this time aligning chunks. It appears the partial chunks were the cause of the crashing.