Why does writing large numbers of files to Truecrypt device cause splicing file error?

Question

Using Linux, I have a whole backup partition encrypted with Truecrypt. I've been using this device for more than a year. Sometimes (but not always) when I copy large numbers of files to the encrypted partition, I receive the error message:

Error splicing file: Input/output error

The encrypted device is then still readable, but not writable.

Why does this happen?

Is this the actual error, or is it confused?

Answer 1

Turns out the drive was on the way to failing. It was relocating bad sectors to a different place on the drive and no doubt failing intermittently.