Why is the latest version of iTunes having difficulty recognising my Apple ID?

Question

This past week, I have been unable to access my iTunes library on my home iMac from my wired Apple TV which was working perfectly well before. No other changes apart from upgrades to Mountain Lion and latest iTunes version as per Software Update. I have now discovered that I cannot sync my iPhone with iTunes and the same thing is happening with my iPod too. There appears to be a problem with iTunes recognising my Apple ID as I am repeatedly being asked to enter my Apple ID but it would not accept my username and password. Interestingly, iTunes, pre-populates the username with my hotmail account (which I rarely use) rather than my me.com address. I have no problem accessing iCloud.
This is incredibly frustrating as I am unable to sync any of my devices with iTunes. iTunes tells me that my home iMac is not an authorised computer and when I do authorise it, it goes through the same loop repeatedly.Tried the usual quitting, restarting, deauthorising then re-authorising my iTunes account, etc.
Anyone has any idea what is happening?

Answer 1

You are not having my exact same problem, but try this:
1. Browse to "C:\Users\<YourUserName>\AppData\Roaming" in Windows Explorer.
2. Rename the "Apple Computer" folder to "Apple Computer-old".
3. Start iTunes
4. Close iTunes
5. Copy the file "iTunesPrefs.xml" from "C:\Users\<YourUserName>\AppData\Roaming\Apple Computer-old\iTunes"
6. Paste the old "iTunesPrefs.xml" into the new "Apple Computer\iTunes" folder iTunes just created (not the one you renamed) under "C:\Users\<YourUserName>\AppData\Roaming\Apple Computer-old\iTunes"
7. Overwrite the new iTunesPrefs.xml with your old copy of the file.
If you don't care about losing your iTunes preferences then you can just do step 2. You can always go back and grab things from the old folder later if you realize you wanted to have your EQ settings, individual track gains, etc...