"However when I try to copy same files to an internal hard drive which uses ext4, the system freezes."
This would be a different bug, as this bug only occurs when removing files.
"My question is, how do I get the fix?"
It looks like the latest karmic kernel release is 2.6.31-17. You might want to try installing that.
If that doesn't work, and assuming that it really is a kernel problem and not caused by something else, you could try the 2.6.32 kernel from lucid's repository, though since lucid is still in alpha stages, it might be best to find out if it really is being caused by the kernel first.
"However when I try to copy same files to an internal hard drive which uses ext4, the system freezes."
This would be a different bug, as this bug only occurs when removing files.
"My question is, how do I get the fix?"
It looks like the latest karmic kernel release is 2.6.31-17. You might want to try installing that.
If that doesn't work, and assuming that it really is a kernel problem and not caused by something else, you could try the 2.6.32 kernel from lucid's repository, though since lucid is still in alpha stages, it might be best to find out if it really is being caused by the kernel first.