Hi Francisco,
This is normal behavior. To perform a batch task (that is, to register a list of target images), StarAlignment must work in either the Register/Match or the Transformation Matrices mode. A batch task is started by executing StarAlignment in the global context, that is not applying it to any particular image (to execute globally, select the StarAlignment interface and press F6, or click the blue ball icon).
The rest of modes can only work in a view context, that is by applying the process to a specific image or preview. For example, if you want to check which stars are being detected in an image, select the Detected Stars mode and apply StarAlignment to that image.
In all cases StarAlignment requires you to specify a reference image, which can be either a view or a disk file.
