Cannot open the application "iTunes" because another user has it open.

For Windows Vista, these are the steps that I took (only one of my accounts needs to run iTunes).

1) Right-click the Quick Launch bar and select Task Manager.
2) Switch the the Processes tab and find iTunes.exe *32.
3) Right-click iTunes.exe *32 and switch to the Security tab.
4) Click the Edit button, which will bring up the Permissions for iTunes dialog.
5) Click the Add button to Select Users or Groups.
6) Click the Advanced button to Select Users or Groups.
7) Click the Find Now button and select the user that IS using iTunes from the Search results and click OK. The iTunes user you selected should then be in the "Enter the object names to select" field.
8) Click OK again to close the Select Users or Groups dialog.
9) Select the iTunes user in the Group or user names list and select "Full control" under the Allow column in the Permissions for <User> list.
10) Select the "Users" Group (this should apply to all other computer users, except Administrators) and select "Read & execute" under the Deny column.
11) Select OK to close the Permissions for iTunes dialog.
12) Select OK to close the iTunes Properties dialog.

That's a huge pain in the ***, and Apple needs to address it, but that should do the trick until then.

/Brian

This looks to be an authority issue for secondary users on XP, Vista or Windows 7. The fix for this is to go to the program files directory, find the itunes application and right click. Select "Run as Administrator". (In Vista and Windows 7, this directory is: C:\Program Files (x86)\iTunes; In XP, the directory is c:\Program Files\itunes)

The unwillingness or inability to cope with user switching on Windows XP (and subsequent flavors) after all this time is absurd.

The question is, is the issue due to Apple being unwilling to bother, or is Windows unable to provide sane behaviors in user switching?

Is Apple concerned a download from iTunes might continue while a different Windows user buys something else from the iTunes Store, or is resource management on Windows so lacking in multi-user orientation it isn't possible to rotate the allocation of say, the sound subsystem, to the current user?

If this is just Apple being stubborn, they are preventing my daughter from buying music while the latest episodes of my video subscriptions download.

Hardly a customer winning strategy...

Windows has fast user switching, but itunes does not take advantage of it. You can tell Apple if you don't like it.
itunes menu > help > provide itunes feedback




But right now, if your daughter wants to buy stuff, finish your video subscription downloads and close itunes on your account. That's the way it works today.
Several users can have WMP open at the same time, and probably be downloading from Amazon although I don't have enough users to try that here. It's certainly not a windows limitation. It's an application problem.