there's no unified error reference that i know of.
this error means that during the StarAlignment phase of the batch preprocessing (image registration) that StarAlignment was unable to match any stars between the reference frame and the frame being processed. this can happen if you accidentally put in a subexposure of a different target, but it can also happen if you have a lot of hot pixels in your subexposures, or you have very soft/misshapen stars such that there are not enough stars detected in either the reference or target, and then no matches can be found.
if you want more information than you ever wanted about how StarAlignment works, open the StarAlignment process and click the little dog-eared page at the bottom of the window. that will open the documentation for SA. it is very technical.
rob
