Ray did a hotfoot build of cart over the weekend to fix this error.
Uninstall eCart from the extension manager, then install it again. When you open DW, make sure the WebAssist Installer Runs to finish the installation, then restart DW.
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These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.