To run the build configuration, you should follow the procedures described in Executing Builds in the Build Administration Console. You should also pay attention to the following:
Make sure the Ant buildfile is in the build directory or is in a location that both Ant and Dimensions CM can find.
If you have targets that need to be preserved, create the Dimensions archives for those targets and then be sure that the Do not preserve targets check box is not selected in the Run Build wizard.