You may see this error if you are attempting to use one of Redgate's command line tools as part of an automated process.

To use the SQL Compare/SQL Data Compare command line you need to login interactively.

A SQL Change Automation license (available as part of SQL Toolbelt) is needed for automated processes (for example when used on a build server). To cover such a case, everyone contributing to this automated process needs to be covered by their own SQL Toolbelt license.