When deploying an external content type created in Visual Studio from a dev to a test or production environment you may get the error:
Error 1 Error occurred in deployment step 'Add Solution': Property 'SiteUrl' contains an invalid URL. Import failed with the following exception message: The Web application at http://mydevwebapp/ could not be found. Verify that you have typed the URL correctly. If the URL should be serving existing content, the system administrator may need to add a new request URL mapping to the intended application.
This issue occurs because the site url you are deploying to is now a different one. E.g. Production instead of dev.
To resolve this simply update the SiteUrl property in the feature manifest to match a valid site url in the target deployment environment:
<?xml version="1.0" encoding="utf-8" ?>
<Property Key="GloballyAvailable" Value="true" />
<Property Key="SiteUrl" Value="http://myproductionwebapp/" />