The Start Transaction from the Database activity package fails when using the v 1.5.0 of the package.
There is an issue with the v 1.5.0 of the UiPath.Database.Activities package that causes the Start Transaction activity to fail.
In order to solve this, use the version 1.4.0 of the Database activity package or upgrade to the latest version (1.9.0 at the moment of publishing this content)