# Refrences:
# https://community.magento.com/t5/Magento-2-x-Technical-Issues/A-technical-problem-with-the-server-created-an-error-Try-again/td-p/114492/page/3
# https://github.com/magento/magento2/issues/16531
# Change "fileUploader" to "imageUploader" in the "formElement" attribute on lines 57, 154 in vendor/magento/module-theme/view/adminhtml/ui_component/design_config_form.xml
# line 57
<field name="head_shortcut_icon" formElement="imageUploader">
# line 154
<field name="header_logo_src" formElement="imageUploader">
# then run the following commands
bin/magento indexer:reindex
bin/magento setup:di:compile
bin/magento cache:clean
bin/magento cache:flush