in each add to cart form ,the option form elements should be named identicly:
<tr>
<td width="225"><strong>MCL-1</strong></td>
<td width="21"> </td>
<td width="228"> </td>
</tr>
<tr>
<td><input name="on0" type="hidden" id="on0" value="Top Plate Line 1" />
Top Plate - Line 1
<input name="os0" type="text" id="os0" size="35" maxlength="35" /></td>
<td> </td>
<td><input name="on3" type="hidden" id="on3" value="Bottom Plate - Line 1" />
Bottom Plate - Line 1
<input name="os3" type="text" id="os3" size="35" maxlength="35" /></td>
</tr>
<tr>
<td><input name="on1" type="hidden" id="on1" value="Top Plate - Line 2" />
Top Plate - Line 2
<input name="os1" type="text" id="os1" size="35" maxlength="35" />
<br /></td>
<td> </td>
<td><input name="on4" type="hidden" id="on4" value="Bottom Plate - Line 2" />
Bottom Plate - Line 2
<input name="os4" type="text" id="os4" size="35" maxlength="35" /></td>
</tr>
<tr>
<td><input name="on2" type="hidden" id="on2" value="Top Plate - Line 3" />
Top Plate - Line 3
<input name="os2" type="text" id="os2" size="35" maxlength="35" /></td>
<td> </td>
<td><input name="on5" type="hidden" id="on5" value="Bottom Plate - Line 3" />
Bottom Plate - Line 3
<input name="os5" type="text" id="os5" size="35" maxlength="35" /></td>
</tr>
on6 and up and os6 and up are not valid option names that paypal will except, to be truthful, i though paypal only excepted on0, os0 and on1, os1, but it looks like they may have expanded the number of options they except.