I took BACKGROUND: URL(images/butbg.gif); out of skin1.css
open skin1/buttons/button.tpl and change
Code:
<TD class="Button" valign="middle" nowrap><FONT class="Button">{$button_title}</FONT></TD>
to
Code:
<TD background="{$ImagesDir}/butbg.gif" class="Button" valign="middle" nowrap><FONT class="Button">{$button_title}</FONT></TD>
that worked for me