onmouseup

Jeg har følgende kode
<HTML>
<HEAD>
<script>
Image1 = new Image(106,30)
Image1.src = \"../graphics/prev_page.gif\"
Image1_2 = new Image(106,30)
Image1_2.src = \"../graphics/prev_page-over.gif\"
Image1_3 = new Image(106,30)
Image1_3.src = \"../graphics/prev_page-down.gif\"
</script>
    <TITLE>[Ingen titel]</TITLE>
</HEAD>
<BODY>
<img src=\"../graphics/prev_page.gif\" ID=\"flipme1\" onclick=\"this.src=Image1_3.src; return true;\" onmouseover=\"this.src=Image1_2.src; return true;\" onmouseout=\"this.src=Image1.src; return true;\" onmouseup=\"this.src=Image1.src; return true;\">
</BODY>
</HTML>

Men reaktionen på at musen går op, sker ikke.... hvad gør jeg forkert?