With version 3.0.0-M1 the syntax for the alt*DeploymentRepository changed from id::layout::URL to id::URL (were using a file protocol here). Additionally the plugin now writes a lock file into the local repository using the id of the repository as base name. Since the plugin seems to interpret id::layout as the id for a legacy parameter value, it tries to write with such a name. Works with Unix, but not with Windows. Here the build fails.
Removing the layout part from the parameter will fix the problem. Therefore this report is more a heads-up for others running into this.