I did all that.
I tried it again just to be sure. Still fails.
I deleted the WinFileCachexxxxx.dat file to no avail. When I said there is none, that refers to my current situation. UE gives the error and no WinFileCachexxxx.dat file has come back yet.
I also closed Dw, renamed my config file, opened the extension manager, removed all extensions, and reinstalled them all. Still fails.
I'm running Dw CS4 on up-to-date Windows 7, Apache 2.2.14, MySQL 5.1.41, and PHP 5.3.1.
Just tried it yet again and only reinstalled UE 4.0.1. Got the same error and it occurs before the WinFileCache file comes back. I cannot find 'CreateEmailMessage_WA.htm' anywhere... Should I delete the 'webassist' directory from my website Root? I think that's the UE stuff.
Related Fact: Maybe my UE install is somehow flawed: eCart Checkout Wizard does NOT stop at the "Email Receipt" section. It skips from the "database settings for storing order information" directly to the "Page Designs". The documentation says "If UE is installed, eCart will provide you with this step for the email receipt". UE is installed as an extension but the Checkout Wizard does not let me do the Email Receipt stuff.