Problem with Upgrading from 1.3.6 to 1.3.8

I’m trying to upgrade my zencart 1.3.6 to the newest version. So far I have failed in every attempt. My biggest problem is data transfer. This is what I did:
Approach I (basically following the instruction)
Download and then upload the latest version, create a new database, edit both configure.php files to point to the server with correct userid and password, export data in a sql file from the existing db and import to the new db, and then using a browser, surf to /zc_install/index.php. This is what I got:
1146 Table 'store2009.products_discount_quantity' doesn't exist
in:
[show fields from products_discount_quantity]

Approach II
Download and then upload the latest version, create a new database, install a new cart, export data in a sql file from the existing db and import to the new db, run the installer again, choosing “upgrade”. In the end I could get nowhere.
I don’t know where I did wrong. Could somebody tell me if there’s a simpler way just to transfer data from one db to another?
Thank you in advance.
:cry:

I posted one message (please see the bottom of this posting) on August 2 seeking help for upgrading problems from zencart 1.3.6. to 1.3.8., but I have not received any response yet. After the post, I searched the forum and found something helpful in DrByte’s response to a query on upgrading problems from zencart 1.1.4. to 1.3.8 back on 28th July 2009. Following DrByte’s advice, I edited the following file (see below) and luckily, was able to move a few steps.

DrByte’s response to Re: Upgrading from 1.1.4 beta to Zen Cart 1.3.8a (28th July 2009)
You'll have to make a fairly small edit to one of the files:
/zc_install/includes/classes/class.installer_version_manager.php
around line 284 you'll see this section of code. Add the 3 extra lines as shown in bold (2 lines in one spot, and one line later):

But after a few steps, I got stuck again with the following message:

1062 Duplicate entry '1-1' for key 1
in:
[INSERT INTO paypal_ipn_address_status VALUES (1, 1, 'confirmed');]
=

Can anybody help me with that?

Many thanks in advance.

-------------------------------------------------------
My original post on August 2, 2009:

I’m trying to upgrade my zencart 1.3.6 to the newest version. So far I have failed in every attempt. My biggest problem is data transfer. This is what I did:

Approach I (basically following the instruction)
Download and then upload the latest version, create a new database, edit both configure.php files to point to the server with correct userid and password, export data in a sql file from the existing db and import to the new db, and then using a browser, surf to /zc_install/index.php. This is what I got:
1146 Table 'store2009.products_discount_quantity' doesn't exist
in:
[show fields from products_discount_quantity]

Approach II
Download and then upload the latest version, create a new database, install a new cart, export data in a sql file from the existing db and import to the new db, run the installer again, choosing “upgrade”. In the end I could get nowhere.
I don’t know where I did wrong. Could somebody tell me if there’s a simpler way just to transfer data from one db to another?
Thank you in advance.