This is usually because of improper nesting of tags (such as and unclosed <P> or <DIV> or <TD>) added inside the button code we originally provided for the Variants/Variations item's Add to Cart button code, like this (problem code in bold):
<form action="https://www.e-junkie.com/ecom/gb.php?c=cart&i=XXXXX&cl=YYYYY&ejc=2" target="ej_ejc" method="POST" accept-charset="UTF-8">
<input type="hidden" name="on0" value="Color"/>
<P>Color:<br/>
<select name="os0">
<option value="Red">Red</option>
<option value="Blue">Blue</option>
</select>
<br/>
<input type="image" src="http://www.e-junkie.com/ej/ej_add_to_cart.gif" border="0" alt="Add to Cart" class="ec_ejc_thkbx" onClick="javascript:return EJEJC_lc(this.parentNode);"/>
</form></P>
Note how the extra <P> added inside the form (just before Option:) isn't closed with a </P> until after the </form> tag -- any <P> or <DIV> that appears between <form...> and </form> should be either closed inside the form or just deleted to fix the button code.
