Ah, now the problem becomes obvious. Notice the syntax highlighting:
$error_required = '<table border="0" cellpadding="0" cellspacing="0" width="858" align="center" valign="top">
<td colspan="2"><a href="screen_print.html" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('screen','','../images/index_r8_c2_roll.jpg',1)"><img src="../images/index_r8_c2.jpg" alt="Screen Printing" name="screen" width="166" height="47" border="0" id="screen" /></a></td>
<td colspan="4"><a href="embroidery.html" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('embroidery','','../images/index_r8_c4_roll.jpg',1)"><img src="../images/index_r8_c4.jpg" alt="Embroidery" name="embroidery" width="168" height="47" border="0" id="embroidery" /></a></td>
<td colspan="2"><a href="sign_making.html" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('sign','','../images/index_r8_c8_roll.jpg',1)"><img src="../images/index_r8_c8.jpg" alt="Sign Making" name="sign" width="167" height="47" border="0" id="sign" /></a></td>
<td colspan="2"><a href="gallery.html" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('gallery','','../images/index_r8_c10_roll.jpg',1)"><img src="../images/index_r8_c10.jpg" alt="Gallery" name="gallery" width="167" height="47" border="0" id="gallery" /></a></td>
<td colspan="7"><a href="testimonials.html" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('testimony','','../images/index_r8_c12_roll.jpg',1)"><img src="../images/index_r8_c12.jpg" alt="Customer Testimonials" name="testimony" width="170" height="47" border="0" id="testimony" /></a></td>
</tr>
</table>';
The problem is that the string literal is single quoted, but you use single quotes within it without escaping them. As such, instead of:
onmouseover="MM_swapImage('screen',
you should write:
onmouseover="MM_swapImage(\'screen\',
as so on.