I don't know why its so hard to include some standart items. I never seen another script where a simple logo needs to study the code and/or tests with a few themes to find out wich of them uses the easiest way to include one.
I mean, why isnt there a default theme wich use all functions in a standart way, so we just need to look into it where it works 100%. Testet 3 themes and in not one of them the logo is shown, and i dont want to include it manually. Maybe the "how to" lines should get a update. And btw to create a folder and insert a logo is also the wrong way i think.

BTW ... bug in effervescence_plus
at line: 179
generateListFromFiles($currentValue, SERVERPATH.'/'.UPLOAD_FOLDER.'/images' , '.png'); ?>

needs a <? to get the function work
Then the upload logo file in uploadet/images/ will shown in the themeoptions menu & when used also on the frontend

...but it still isnt the right way i think!

First, differently than other CMS Zenphoto leaves a lot more freedom to the theme developer. A logo is not a standard item, so it is up to the theme developer to setup a easy way to replace or add one.

Otherwise all is HTML and CSS which you need knowlegde in any case.

Besides that it seems you discovered a bug in the theme as I can reproduce the failure. The line you cite makes me thing you are not using the latest release though. The function related is in the theme's function.php line 245-261).
Anyway, I have opened a ticket for this as my colleague is more familiar with this theme.