I used Clonezilla to copy an ext4 1.5 terabyte disk to a 4 terabyte disk. But when I try to use Gparted to grow the partition to fill the 4 terabyte, it fails. Repeated trials show it only allows me to fill to half the disk (2 terabytes); otherwise I get an error message saying "see details", although there are none. I suspect that Gparted is operating 32 bit, even though I am running it from a live Ubuntu 64 bit 14.04 media edition DVD. If Gparted included with 64-bit Ubuntu is limited to 2 terabyte due to 32-bit arithmetic, what else can I use to grow the partition? Is there a 64-bit Gparted or equivalent?
Your filesystem has MBR (Master Boot Record), in MBR maximum partition size is 2TB(tera byte) only, so that's why you are not able to do this.
To make the system capable of this, you need to replace your MBR with GPT (GUID Partition Table). It allows you to create one partition up to 2PB(peta byte). To replace you can read this link : How can I change/convert a Ubuntu MBR drive to a GPT?