Magento2 - Error when trying to edit theme in Content>Design>Configuration

[arunav949]

Hi - I am using MAgento2 and the Lumia theme. I am not sure what changes I made, but when I tried to edit the theme from Content > Design > Configuration page last week, I got the following error:

There has been an error processing your request

Exception printing is disabled by default for security reasons.

Error log record number: 309994647556

I took a look at the file in var/report and can't figure it out - this is the start of the message - don't want to paste the entire file here!

Any help would be greatly appreciated as I can't open that page at all anymore!

Thanks much

The configuration parameter "componentType" is a required for "swatch_image" component.";i:1;s:8169:"#0 /home/<USER>/public_html/vendor/magento/framework/View/Element/UiComponentFactory.php(361): Magento\Framework\View\Element\UiComponentFactory->mergeMetadataItem(Array, Array, false)

#1 /home/<USER/public_html/vendor/magento/framework/View/Element/UiComponentFactory.php(361): Magento\Framework\View\Element\UiComponentFactory->mergeMetadataItem(Array, Array, false)
#2 /home/<USER>/public_html/vendor/magento/framework/View/Element/UiComponentFactory.php(361): Magento\Framework\View\Element\UiComponentFactory->mergeMetadataItem(Array, Array, false)
#3 /home/<USER>/public_html/vendor/magento/framework/View/Element/UiComponentFactory.php(272): Magento\Framework\View\Element\UiComponentFactory->mergeMetadataItem(Array, Array, false)

....

{main}";s:3:"url";s:129:"/admin5203/theme/design_config/edit/scope/stores/scope_id/1/key/19d41241bb329e710129bb54a747c9c2e6171a5712132237cd4db55739e99b24/";s:11:"script_name";s:10:"/index.php";}

[Tom Robertshaw · Accepted solution]

One person has shared this solution on stack exchange. Would you like to check that Magento_Swatches hasn't been disabled? https://magento.stackexchange.com/a/161693/26

[Legide34]

Hi everyone, i run a magento 2.2.2 version.

i have a similar problem when creating my first magenta theme. i followed all the steps for creating a theme structures et files. still when a copy my theme folder in app/design/frontend/ i got an error. i checked the log and see i was missing media/preview.jpg. i added that, restarted the server and  then got another error on registration.php 

{"0":"Warning: Cannot modify header information - headers already sent by (output started at \/Applications\/MAMP\/htdocs\/Magento\/app\/design\/frontend\/mytheme\/ultimatetheme\/registration.php:1) in \/Applications\/MAMP\/htdocs\/Magento\/vendor\/magento\/framework\/Stdlib\/Cookie\/PhpCookieManager.php on line 148","1":"#0 [internal function]: Magento\\Framework\\App\\ErrorHandler->handler(2, 'Cannot modify h...', '\/Applications\/M...', 148, Array)\n#1 . since the backend turn blank page. i was able to get to the backend when i deleted the theme folder. 

thanks in advance

[Legide34]

Solved.