pop窗口为什么弹出一次就不弹出了,该如何解决

var oPopup = window.createPopup();var popTop=0;function popmsg(msgstr){var winstr="<div style='height:172;width:241;overflow:auto;'><table style=\"border: 1 solid  #6D93C8\"  width=\"241\" height=\"172\" border=\"0\" cellpadding=\"0\" cellspacing=\"0\"   >";winstr+="<tr><td align=\"center\"  valign=\"top\"><table width=\"90%\" height=\"110\" border=\"0\" cellpadding=\"0\" cellspacing=\"0\">";winstr+="<tr><td valign=\"top\" style=\"font-size:12px; color: #6D93C8; face: Tahoma;line-height:20px;\" >"+msgstr+"</td></tr></table></td></tr></table></div>";oPopup.document.body.innerHTML = winstr;popshow();}function popshow(){     if(popTop>172){        clearTimeout(mytime);         oPopup.hide();        return;    }          else{    oPopup.show(screen.width-250,screen.height-172,241,172,document.body);    }         popTop=popTop+50;           var mytime=setTimeout("popshow();",50); }