"iTunes has encountered an error.." Help! I've tried EVERYTHING.

Question

I am running WIndows XP Media Center SP3 on an aging HP PC (Pentium 4).
In the past, iTunes (v. 7, I believe) worked just fine on my PC with no problems.  For a long time, I did not have a 'need' to upgrade the software because it worked fine the way I liked it. However, after purchasing an iPod approximately 6 months ago, I tried to upgrade iTunes to a newer version, but upon installation, received the error message "iTunes has encountered an error and cannot continue" and have not been able to successfully update since. After tweaking and a lot of trial and error, I was able to get as far as an early version of iTunes 9 before getting the messages again.  As I have recently acquired an iPhone (and want to update to OS 5), it doesn't help me if I can't update to the latest version of iTunes (10.5). I'd like to experience the full functionality of my new phone, and I NEED iTunes for that.
So far: I have repaired, removed, installed, uninstalled, removed all traces of (including from the registry) any and all versions of Quicktime and iTunes (and all related programs: Bonjour, MobileMe, Apple Support, etc) and NOTHING has worked.  I've removed codecs and other programs I thought may have contributed to the problem, but no luck. I've uninstalled my anti-virus software, no luck. I've used registry cleaners (CCleaner and Registry Crawler) to find and remove rogue files/extensions, etc. Still nothing.  At one time, I *was* able to get a standalone version of Quicktime to work (but not at the same time as iTunes), but again - a MUCH older version than the current one. This doesn't help me, as the moment I try to upgrade either Quicktime OR iTunes (or both) to get the most recent version(s), I again receive the same error... "iTunes/Quicktime has encountered an error and cannot continue."  I've even tried extracting files individually (using WinRAR) from the iTunes 10.5 installer package, and installing them one at a time.  Still no go.
I have seen MANY people with the same problem I have - yet I've tried EVERY posible solution (short of re-installing Windows) I can think of, or have found, or that has been suggested in these forums and elsewhere - and NOTHING has worked for me.  Can anyone help me? Surely there must be SOME solution?
The data Microsoft gives me when the error message(s) come up is as follows:
iTunes:
AppName: itunes.exe           
AppVer: 10.5.0.142           
ModName: unknown
ModVer: 0.0.0.0    
Offset: 001be6f6
Quicktime:
EventType : BEX    
P1 : QuickTimePlayer.exe    
P2 : 7.71.80.42    
P3 : 4ea5c6ef    
P4 : QuickTimePlayer.dll    
P5 : 7.71.80.42    
P6 : 4ea5c6d5
P7 : 00005b6d    
P8 : c0000409    
P9 : 00000000
Any information is greatly appreciated.

Answer 1

iTunes:
AppName: itunes.exe          
AppVer: 10.5.0.142          
ModName: unknown
ModVer: 0.0.0.0   
Offset: 001be6f6
Quicktime:
EventType : BEX   
P1 : QuickTimePlayer.exe   
P2 : 7.71.80.42   
P3 : 4ea5c6ef   
P4 : QuickTimePlayer.dll   
P5 : 7.71.80.42   
P6 : 4ea5c6d5
P7 : 00005b6d   
P8 : c0000409   
P9 : 00000000
That's consistent with another application (other than QuickTime) having dropped old QuickTime componentry in non-standard locations on the PC.
So we'll go looking for the older QuickTime componentry in the most common locations for it to be stashed.
First we'll need to change some view options on the PC.
1. Open My Computer from the desktop or Start menu.
2. In the Tools menu, click Folder Options.
3. Click the View tab.
4. In the "Advanced settings" pane under "Hidden files and folders" make sure that the "Show hidden files and folders" option is selected, and the "Hide extensions for known file types" option is unchecked.
5. Click OK.
Now in My Computer, open your C drive.
Open the "Windows" folder.
Open the "system32" folder.
What files and/or folders can you see in there with QuickTime in the file/folder name? (In a standard installation of QuickTime, you should see precisely two files ... QuickTime.qts and QuickTimeVR.qtx ... and no QuickTime folders whatsoever.)