Software Update and iTunes

On my mac book pro I keep getting messages that there is a software update. But every time I download it halfway through it closes and says there was an error. Is it necessary to update? Also my iTunes is acting odd, it suddenly closes after I open it. I tried fixing it by deleting the files and starting it up again. At first it helped but now it has started closing unexpectedly again.

Have you tried downloading iTunes from Apple's website as opposed to getting it through Software Update?