Hi,
If the configuration is saving right without image upload and generates a problem when uploading an image, it could be a server-side conflict.
The configuration is a big form and send a lot of parameters.
When uploading a file, the form should send data in a specific format, compatible with file upload.
The problem is that some web hosting have some limitations, some security checks which are quite too restrictive.
So the server refuse the page call because the form is too high for him (with the number of fields in the specific "post format").
The only solution I see is to upload the image by FTP and change the option in the database.
With the integration of HikaMarket features into HikaShop, it would be possible to have a asynchronous upload of the image and have a configuration compatible with your web hosting, but this integration is not planned before several weeks/months.
Regards,