The default skin is changed to "terrace", ext/dhtmlxscheduler_dhx_terrace.js is removed. To change the skin back to the classic one, just include the related CSS file (codebase/dhtmlxscheduler_classic.css). For more details check Skins.
Scheduler detects the used skin, based on the name of the CSS file, so if you are using a custom skin (which is not based on "terrace"), rename its css file to dhtmlxscheduler_skin name.css. Also, you can disable the skin auto-detection by adding the following line before scheduler.init:
DHTMLX Scheduler .NET V.4.0 Enterprise
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