Error when Enter is pressed for Search in IE8

After typing in  a search word and pressing Enter:
Message: 'document.getElementById(...)' is null or not an object
Line: 118  (below)    /default.aspx

<input name="ctl00$wpm$HomePage$ctl00$SearchPhrase" type="text"
id="ctl00_wpm_HomePage_ctl00_SearchPhrase"
onkeydown="if(event.which || event.keyCode){if ((event.which == 13) || (event.keyCode == 13)) {document.getElementById('ctl00$wpm$HomePage$ctl00$SearchButton').click();return false;}} else {return true}; " />

<input type="submit" name="ctl00$wpm$HomePage$ctl00$SearchButton"  
onclick="if(Page_ClientValidate('Search')){window.location='/Search.aspx?k='+encodeURIComponent(ctl00_wpm_HomePage_ctl00_SearchPhrase.value);}return false;WebForm_DoPostBackWithOptions(new WebForm_PostBackOptions(&quot;ctl00$wpm$HomePage$ctl00$SearchButton&quot;, &quot;&quot;, true, &quot;Search&quot;, &quot;&quot;, false, false))"
id="ctl00_wpm_HomePage_ctl00_SearchButton"  />

Do the dollar signs have anything to do with it:

ctl00$wpm$HomePage$ctl00$SearchButton
ctl00_wpm_HomePage_ctl00_SearchButton  << id of Search button