Hi fellow AC users:
I just want share my story of Windows Update updating KB954430 update.

Problem:
Our MAIN comp was failing to start AC and its other programs such as Amazing Utilities, Amazing Backup, etc. We have version 5.0.26.
When I double click AC shortcut or access it through programs menu, AC application was trying to install and was poping up Error 1306 window. Exact message was:
"Error 1306. Another application has exclusive access to the file 'C:\AmazingCharts\codes.ldf'. Please shutdown all other applications, then click Retry."
with Retry and Cancel button.
Clicking Retry was going nowhere. Clicking Cancel was generating "Fatal error during installation." message window.

Even after restarting the comp problem persisted.

Background:
A day before I tried to run Windows Update. "Security Update for Microsoft XML Core Services 4.0 Service Pack 2 (KB954430)" update was failing to install. It was not installing for some reason.
Its FIX involved deleting MSXML4.dll and MSXML4r.dll files under %systemroot%\system32 folder.
After deleting above files I ran Windows Update which installed KB954430 update.
BTW, this happened on 5 of our networked client comps and MAIN comp. All of our comps have Win XP pro.
FIX installed KB954430 update on all of our client comps but not on MAIN comp. It looked like FIX went through fine on MAIN comp as there were no error messages while installation. Rerunning Windows Updat did not show any pending updates.

Now, next day morning AC was failing to start and creating above mentioned "Problem".

Solution:
Upon looking into %systemroot%\system32 folder MSXML4.dll and MSXML4r.dll files were missing and "Add or Remove programs" list did not have KB954430.
I was mislead by Window Update info. It did not report KB954430 installation failure. I did not bother to check for these DLLs as there were no error
Any how, I manually downloaded and installed this particular update which installed above DLLs. This time I verified existence of these DLLs in %systemroot%\system32 folder and listing of KB954430 under Add or Remove Programs list.

Bingo! AC was running like race horse.