Why do I get a HTML 500 error?

Good day Ray,
When I added two e-cart buttons this morning and "put" the page onto the server I got a HTTP 500 error. This was on the MOCA-Mart page: http://lotcs.org/WA_eCart/moca_mart.php. The Cootie Depot store is also affected. This is exactly what I did to add my e-cart buttons. I went to the "WebAssist" menu bar at the top of the page in Dreamweaver CC. I selected "Add to Cart Button" and then I select the "Cart.php" file. Then I went to Bindings and input the Item number, size, color, name and title. Then I selected the type of button and hit OK. Then, because it showed up in the center, I added a "<p align left> tag within the code below. Finally I added the options that I needed and then "put" the file on the server. After which I received the HTTP 500 error. Thanks for your help!
Dale

<form name="eCart1_93_ATC_AUX-2007M" method="POST" action="<?php echo $_SERVER["PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".htmlentities($_SERVER["QUERY_STRING"]):""; ?>"> <p align="left">
<input type="hidden" name="eCart1_93_ID_Add" value="AUX-2007M" >
<input type="text" name="eCart1_93_Quantity_Add" value="1" size="4" />
<select name="eCart1_93_Size_Add">
<option value="Small" selected>Small</option>
<option value="Medium">Medium</option>
<option value="Large">Large</option>
<option value="XL">XL</option>
<option value="2XL">2XL</option>
<option value="3XL">3XL</option>
<option value="4XL">4XL</option>
</select>
<select name="eCart1_93_Color_Add">
<option value="Black" selected>Black</option>
<option value="Red">Red</option>
<option value="White">White</option>
</select>
<input type="text" name="eCart1_93_Name_Add" value="Name">
<select name="eCart1_93_Title_Add">
<option value="Title" selected>Title</option>
</select>
<input type="image" src="../WA_eCart/Images/Desert Spice/Btn2_EN_addtocart.gif" border="0" class="eC_ImageButton" value="Add to Cart" name="eCart1_93_ATC">
</p>
</form>