eCart Add to Cart - Error "At line 907...has no properties"

Hello

PHP/MySQL server model
eCart 4.5.2 (uninstalled and reinstalled)
DW CS4 (on WinXP SP3)

I can successfully connect to my remote database.
I have added a Cart.
However, when I click the Add to Cart icon, and choose Look up item ID from recordset I get the error

"While executing onClick in WA eCart AddToCart.htm, the following JavaScript error(s) occurred:
At line 907 of file "C:\Program Files\Adobe\Adobe Dreamweaver CS4aConfiguration\Commands\WA eCart AddToCart.js":
document.generalWP.document.column.options[document.generalWP.document.column.selectedIndex] has no properties"

(A previous thread (showthread.php?p=27737&mode=linear&highlight=At+line+907#post27737) also mentioned this, but no solution was given.)

Incidentally, the path shown in the DW error message above is incorrect, as the AddToCart.js file mentioned is actually in
C:\Documents and Settings\user_name\Application Data\Adobe\Dreamweaver CS4\en_US\Configuration\Commands

I don't expect that this path error is helping much...

For info, line 907 in AddToCart.js reads
var ColumnName = document.generalWP.document.column.options[document.generalWP.document.column.selectedIndex].text;


Also, could you clarify for me if it's OK for the WA_eCart directory to be outside the webroot (although it's in the root of the local site, there is a webroot folder that forms the root of the remote site -- you can just see this in the site structure at the right-hand side of the attached file).

I have uninstalled and reinstalled the eCart 4.5.2 extension, and deleted the DW cache file (both of these were done while DW was closed).

I'd be really grateful for help. I've been tearing my hair out for days over this, and the project's running very late.

Many thanks
Alistair