The new Registax version it is better for stacking the B/W raw solar images, here some news and advices
Open Registax.
1-. Click on select and open your captured file, avis, bmp etc.
2-. Remove the green mark on "Automatic".
3.-Select the alignment box size >64 and < 258.
4-.Click on any alignment feature (highly contrasted areas, a sunspot, plages or any good Prominence etc)
5-.On the "Quality estimate" box select Compress (it works great with B/W images)
6-. Select >90% quality.
7.- Click on Align
Stacking part 2