Intuit recently released R3 of Q2006. I tried the One-Step Update, which failed with a message that the patching engine experienced a problem. No surprise; I almost always have to download the manual updates. So, downloaded R3 which is only 1 MB. Still got the patching engine error - AND could no longer do any on-line activity in Quicken. No error message, just a very rude dump completely out of Quicken back to the WinXP desktop.
Did a super-validate. Q2006 found an error in the QEL - again, not a surprise. Happens frequently and not the actual problem. Didn't fix it.
Uninstalled and re-installed Q2006. No dice; still no on-line activity, no One-Step Update. Followed Intuit's on-line help (yeah, right - what an oxymoron) which suggested uninstalling, using MSCONFIG to turn off all services except the MS Installer, reboot and install. That didn't help.
Uninstalled again and rebooted. And checked the directory where Q2006 was installed. Even after an uninstall, I found dozens of .dll's hanging around, and the programs like QW.EXE still here. I deleted the entire contents of the folder and all subfolders. (I store data on another drive partition.)
Turned all the services back on, rebooted, reinstalled. Ran One-Step Update and it worked perfectly. On-line activity was back, registers synchronized.
So, moral of the story is - don't assume the Windows Add/Remote Program or the Quicken Uninstaller works. Left over junk from previous versions or previous releases can hang around.