1100 - Target '%s' already defined.

Description
An attempt was made to define a target that was already defined. Each unique targets must be defined only once. Redundant definitions are not permitted.

Targets should always be defined before use to prevent unexpected implicit definitions preventing explicit subsequent definitions.
Example
Config:
Unity( 'Unity1' ) { .UnityInputPath = 'Code\' .UnityOutputPath = 'Tmp\' } Alias( 'Unity1' ) // Target already defined { .Targets = 'Unity1' }
Output:
c:\Test\fbuild.bff(6):(1) FASTBuild Error #1100 - Alias() - Target 'Unity1' already defined. Alias( 'Unity1' ) ^ \--here
Fix:
Unity( 'Unity1' ) { .UnityInputPath = 'Code\' .UnityOutputPath = 'Tmp\' } Alias( 'MyAlias' ) { .Targets = 'Unity1' }