While downloading OpenCV2.4.2 in 12.04, I get the following error message:

bzip2: Compressed file ends unexpectedly;
   perhaps it is corrupted?  *Possible* reason follows.
bzip2: Inappropriate ioctl for device
   Input file = (stdin), output file = (stdout)

It is possible that the compressed file(s) have become corrupted.
You can use the -tvv option to test integrity of such files.

You can use the `bzip2recover' program to attempt to recover
data from undamaged sections of corrupted files.

tar: Child returned status 2
tar: Error is not recoverable: exiting now