Do you have some more details? A stack trace? Gradle version? Does -a work from the command-line with the same build?

It's how the command is executed. The space is missing between task name and -a.

beluga:demo etienne$ gr -v

------------------------------------------------------------
Gradle 0.9-20101019080116+0400
------------------------------------------------------------

Gradle build time: Tuesday, October 19, 2010 8:01:16 AM MSD
Groovy: 1.7.5
Ant: Apache Ant version 1.8.1 compiled on April 30 2010
Ivy: 2.2.0
JVM: 1.6.0_20 (Apple Inc. 16.3-b01-279)
OS: Mac OS X 10.6.4 x86_64

Executing command: ":build-a"

FAILURE: Could not determine which tasks to execute.

• What went wrong:
  Task 'build-a' not found in root project 'demo'. Some candidates are: 'build'.

• Try:
  Run gradle tasks to get a list of available tasks.

BUILD FAILED

Total time: 3.975 secs

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