Just a follow up here:
The Developer Jason Schuller from Press75.com was actually very helpful and responsive by looking into the matter. Thanks for that, Jason.
Here is the fix that I found:
– Deactivate Acquisto theme
– Completely uninstall Acquisto theme
– Deactivate Cart66 Plugin
– Completely remove Cart66 Plugin (From the backend Cpanel!)
– Reinstall Cart66
– Activate Cart66
– Reinstall Acquisto Theme
– Activate Acquisto Theme
– Reset Theme Options:
Appearance –> Theme Options –> Reset Options (bottom left corner of theme options screen)
Not sure why exactly, and I can’t explain it, but this fixes the issue of receiving the cheatin’ uh error message when trying to use the media uploader.