Just found this, hope it helps someone :)
FYI: I'm running iTunes 10.5 on Windows 7 (64 bit), but apparently this works on Mac OS too......it may be due to upgrading o 10.5 last week, but I'm not certain that's what caused it. Anyway, on to the fix!
Symptom:
when you do anything in iTunes Store, itunes seems to hang showing "Accessing iTunes Store" in the banner.
Fix:
- Open iTunes - go to the top bar, click the 'Store' drop down menu
- Then click 'De-authorise this Computer'
- Enter your password
- Close & relaunch iTunes
- Click 'Store' again then click 'Re-authorise this Computer
- Enter password
et voila, the store should work properly again!
Source: