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 can 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 Version Control System on every build - although this can have performance implications for larger databases.