Hi, folks!
I've been having this problem with iTunes for months now. When I saw Spyware Doctor come up as a possible culprit, I went to pctools.com and did some searching to see if PC Tools is aware of any iTunes issues. Lo and behold, I give you this:
http://www.pctools.com/kb/article/protection-software-itunes-is-not-working-corr ectly-with-pc-tools-protection-software-installed-fixed-323.html
So--if you have Spyware Doctor with Antivirus (like I do), there is interference with "PC Tools LSP." They have a fix for this, and you can read it here, but it's basically this:
1) log into your pctools account
2) click on the license for your Spyware Doctors program
3) Under "Supported PlugIns," uncheck the "email guard"
4) Open up Spyware Doctor, then run a smart update. (You might not get any updates, depending on when you last updated the program. I didn't get anything.)
5) Reboot your computer.
This should fix things! I was skeptical about this because I didn't have to update Spyware Doctor at all, but this did the trick, all right. For some of the folks who have this problem, it just might be Spyware Doctor's fault (or PC Tools Internet Security).
Hope this helps!