Currently Bamboo does not support CVS Alias Modules as bamboo expects there to be a directory with the specified checkout module name.

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There is a current workaround using ampersand modules:

The configuration supported by Bamboo requires you to create a module with the same name as the ampersand module (it can be empty) to specify as the root of the ampersand module

eg.
create a module allbuilds
define an ampersand module
allbuilds allbuilds &project2 &project2 &project3