Just to let you know that I have copied from one usb drive to another with no problems.
I use XP SP2
2 x USB drives into two USB ports on my laptop.
The one thing that I do that is very different is that I remove my partitions from my drives and do not format the WBFS partition with NTFS. I have unknown partitions in Windows and then use WBFS to format the partitions.
Both drives actually have two partitions each, the first is unknown and the second is FAT32 as Ihad problems with NTFS.
WBFS partition must be the first partition on the USB drive.
My suggestion is to remove all partitions from your new drive, set the unknown partition as primary and active and do not format with windows.
Run WBFS and format the partition.
I run on 500GB drives and I don't think the Wii can handle 1.5TB but that may just be a rumour. Try a 500GB partition and use that instead.
ALSO on the 'new' dive, have you tried to install anything and run it? This would test that the partitioing is correct before you try and use WBFS to copy.
I use uloader in HBC to run from my USB drive although I don;t see whay that should make any difference. SO summarry:
DO not format
Partition and do not format
Make partition primary and active (Windows Disk manager)
Format 1st partition with WBFS
Use WBFS to copy across.
Hope this helps - let me know if you follow the above and still no luck.