After update from build 7.7.3045 to 7.7.3054 the calendar object disappeared and the following error is reported from the WebResource.axd:
"Unable to set property 'innerHTML' of undefined or null reference" on ;$2f.firstChild.innerHTML='';
Thanks for reporting the issue. It's fixed now in build 7.7.3058 (see the sandbox at http://www.daypilot.org/sandbox/). The fix will be included in the next release.
The bug affected the CssOnly="false" mode. The workaround would be to switch to CssOnly="true" and use the traditional CSS theme (Theme="calendar_traditional"). See also: http://www.daypilot.org/demo/Calendar/ThemeTraditional.aspx