Missing grid lines for scheduler

Why the smal (light gray) scheduler gridlines for each hour and half hour do not appear at all on the control?

<script src="Scripts/dhtmlxScheduler/dhtmlxscheduler_minical.js" type="text/javascript" charset="utf-8"></script>
<link href="Scripts/dhtmlxScheduler/dhtmlxscheduler.css" rel="stylesheet" />

the calendar grid is defined with this class in dhtmlxscheduler.css

.dhx_scale_holder { background-image: url(imgs_dhx_terrace/databg.png); }Please check whether the bg class is overriden on your page, and make sure that you’ve copied image files