I encountered the same problem (on v8.0.2) and figured out the cause.  When downloading for the first time, my antivirus (Trend Micro) was interfering with the download.  I stopped Trend (Task Manager -> uiSEAgnt.exe) and then I could download the whole blockchain without an error.  {This is easily reproducable.}   Once you get the whole blockchain, you can run Bitcoin-QT with antivirus just fine.  It has to do with the fast IO during the initial download.

At first, I was getting the "FAILED TO READ BLOCK" error randomly even 1000 blocks or so.  Start it up, and a few thousand more blocks come down - then get error again.

In the log file C:\Users\Gateway\AppData\Roaming\Bitcoin\debug.log

...
received block 000000009342a7b5d434088a48d94dc05ca2b8543f11d8042c4fa2a32f3cfad5
Unable to open file c:\bitcoin\datadir\blocks\blk00000.dat
ERROR: CBlock::ReadFromDisk() : OpenBlockFile failed
*** Failed to read block
connection timeout
ERROR: AcceptBlock() : AddToBlockIndex failed
ERROR: ProcessBlock() : AcceptBlock FAILED
received block 00000000b4faa2facc1e5f54978b5c4cc770457d0ce921ac7c8a45d766e0858a
addcon thread interrupt
dumpaddr thread stop
SetBestChain: new best=000000009342a7b5d434088a48d94dc05ca2b8543f11d8042c4fa2a32f3cfad5  height=366  log2_work=40.519658  tx=374  date=2009-01-13 19:56:49 progress=0.000008
msghand thread interrupt
net thread interrupt
connection timeout
opencon thread interrupt
Flush(false)


I started up an old version 6 Bitcoin client.  It too got the error; which is odd since I've used it on the same computer last year.  Then, I stopped the Antivirus and it downloaded the whole blockchain fine with version 8.0.2.

Again, once you get the full download, I have not seen the problem with the Antivirus running.  The IO is much slower with the higher blocks.

Hope this helps others...