jeking:
I had been using the more recent version from the ZC 1.5.4 series. I tried the 1.5.5 version but same problem.
Attached are how I've got the product set-up.
My confusion is this is not an SBA attribute, so it should just ignore it. I feel like I missing something that expresses this.



Well, I would actually say that something else is installed that is interfering.
Reason is, the error shown on the previous post at line 28 of includes/templates/YOUR_TEMPLATE/templates/tpl_modules_attributes.php for the version of the file between April and about June of this year began passing the database credentials for generation of the queryfactoryresult class variable. This only became necessary in ZC 1.5.5 because of changes made to includes/classes/db/mysql/query_factory.php. In previous versions of ZC, that variable was not needed, and in fact if it was passed to the function, would be ignored by a default install because it would be an excess parameter that is/was not handled by ZC and therefore would not cause a problem. If though, that zc file were replaced by some other plugin, the additional variable may become necessary and if the template file of the current set was used, it would attempt to pass it properly and not through an error.
That said and as questioned, the line 28 code would only be run if the product for any of many different reasons was not to be displayed as a SBA tracked product, one that matters specifically to adding the product to the shopping cart is whether the products_id is listed at all in the products_with_attributes_stock table (all such entries appear in the admin control screen for SBA under the catalog dropdown).
Now, the other thing, which was an issue with ZC 1.5.4, is that there are error messages not pushed to the screen when there is a problem with adding product to the cart. Unfortunately I don't recall the specific work around that was necessary, but it may be addressed in the known issues with ZC 1.5.4. I do know that Ajeh had weighed in on the matter in one of the past/previous threads.
Beyond that, SBA doesn't evaluate any of the settings shown in the previous images in relation to non-SBA tracked product (products_id not identified in the PWAS table), so the issue would not specifically be with SBA processing, but instead something else that has been done/installed and that a file modified by SBA is showing the result of that other change.
It is something I have wanted to remove so that code like what is found on your version of the template file is no longer "necessary" as it was added at one point to make the file "easier" to follow and require less alternate/additional code. Now it just seems to complicate modification and be seen as the reason for some other mistake unrelated to SBA.