When loading the Answer Customer action in Lightning Experience, you are encountering an error similar to the following.
In version 4.51 of Email to Case Premium, Internet Creations introduced functionality for the Answer Customer action that allowed the component to resize based on the content. Unfortunately, this method is no longer supported within the Lightning Experience following the Spring 19 release of Salesforce.
To avoid this error with the Answer Customer action, upgrade to version 5.34 or later of Email to Case Premium through the AppExchange. The Answer Customer action can no longer automatically resize its height within the Lightning Experience, and will load with a default height of 650 pixels.
The following instructions allow you to create a custom action to load the Answer Custom action with a height different than the default.
If you require assistance with upgrading, please open a support case, include your Org ID and grant login access to Internet Creations Support.