Occasionally, particularly if you are saving the deployment script, the TeamCity build process will not adequately clean out the working directory, causing a build error about a duplicate object.

This can be fixed by accessing the build agent from 'Agents' and using the 'Clean sources on this agent' action under 'Miscellaneous'. 

If this occurs repeatedly, you may want to edit the build configuration and go to Version Control Settings, and switch on the 'Clean build' advanced option, which will ensure you get an entirely fresh copy from your VCS on every build - although this may have performance implications for larger databases.