In the Curves adjustment layer Properties box there are numeric entry boxes for changing input and output values. The first few times I experimented with changing the output values of a selected point in the R, G, & B channels, all went well. Now, although I believe I am using the same method, I can only access the input value box. The moment I click on the output value box both boxes black out and no entry is possible. I'm using the Windows version of Photoshop CC, so Tab doesn't work to get from the input to the output box. I have tried resetting the Preferences for Photoshop and that seemed to work once, briefly, but now that makes no difference.
I have fixed the problem with Adobe Customer Support Chat. The solution was to delete the Adobe Photoshop CC Settings folder. With Photoshop closed, open the Start menu and type %AppData% in the search bar (Windows 7); this takes you to the Roaming folder where you then navigate to the Adobe folder and the Adobe Photoshop CC folder. We removed the Adobe Phototshop CC Settings folder by dragging it to the desktop. Once it was established that this fixed the problem, the folder was deleted from the desktop.
Message was edited by: C55279 Problem solved