Two windows come up when you run the DP. There is the one where you specify the target star (can't remember the real name) and the one where you specify the FITS locations, add the darks/flats, etc. The first window is not coming up.
I looked at Dennis's guide. Section 7.2 - When you click on the DP icon, two windows should appear - the CCD Data Processor and the DP Coordinate Converter. The DP Coordinate Converter window has stopped appearing on my system!
I had not tried to "If you are wanting to add new FITS Header Info, go to the FITS Header Updates section, check General, and then if needed, click the Protractor icon" because I did not think I was trying to update the FITS header; I was simply trying to input the target name in the DP Coordinate Converter window so I could ensure the AIRMASS figures appeared in the measurements table. Now I've checked the General checkbox in the FITS Header Update, the DP Coordinate Converter window is appearing again. Not sure how/why the checkbox got unchecked, but it was not obvious to me that a checkbox in this area was causing a window not to appear. It appeared to me we were just miscommunicating about the problem, which all started with me misnaming the offending window (target star window) because I could not see the window to remember its name.
No problem Gary. Glad all is worked out now. The airmass numbers are added to calibrated image fits headers and then extracted by multi-aperture from the fits headers later. That allows the calibrated images (with the updated fits headers) to be further processed at any time in the future as well.