I went back over my data and found 2 more panels from this CaK run and this time was able to persuade Microsoft ICE to construct a mosaic.
This is the first CaK mosaic Ive done with the 1000/102mm refractor in CaK and there is now a lot more detail near the Sunspots including white areas of intense magnetic activity. I also used masking for the first time in Registax 6 so as not to oversharpen the black central umbrae of the sunspots. Seems to have worked well.
Think I will need about 9 panels to come closer to successful mosaic imaging each time.
Click on the image to enlarge.