I have tried to upgrade our ZenCart from v1.3.7 to v1.3.8a without much success.

Applying or not the customizations that I have done, I'm getting the same results – when the customer try to download his/hers online purchase, the download button appears, however it is linked to the wrong location (the download is unsuccessful). I have checked the configure.php file and everything seems to be fine to me.

Those are the steps that I have tried:
1 – Unzip a copy of the new version of Zen Cart, upload it to our webserver into a "store-temp" folder, and install the new version into a separate database, and include the Demo products. It worked perfectly.
2 – I have changed the configure.php file (on both include folders) to point to our current database and I executed again the zc_install/index.php and now I choose “Upgrade”. Everything went well without any noticeable issues.
3 – The “out of the box” ZenCart store (without my customization) seems to be working but when the custom login and try to download he/she gets the issue described initially.

I have tried many different approaches for this upgrade (and this one is the simplest one) and I'm getting the same result.
Any suggestion is appreciated.
Thanks!