The default project directory match for case-insensitive OSs is unstable.
see also http://www.mail-archive.com/user@gradle.codehaus.org/msg02804.html

When using Gradle on MacOS X with an uppercase letter in the path, one will get
"Could not select the default project for this build."
showing the lowercase dir name.

Now, there are some MacOS X gotchas involved here. It happens that even though the dir is in uppercase - and so shown in the Finder - a pwd may show the lowercase name if you switched to it via cd lowercasename.
BTW: the same build that throws the error above, worked fine for me when started from inside IntellijIDEA.

To get around the problems of build ok/failing dependent on how I navigated to the dir I had to rename my dirs to all-lowercase.

Suggestion: Gradle should check the default project dir ignoring the case (at least when on MacOS or Windows).