Let me add to this. I have another WordPress 4.2.4 site (worldslargest.us). With NextGEN Gallery 2.1.2 activated, I was unable to activate any of the plugins I attempted to activate. Once I deactivated NextGEN, the others activated just fine. I activated NextGEN last. I was able to add images without problem.
I then tried the same thing with roundamerica.com. I deactivated every plugin. I then activated NextGEN Gallery only, and I was able to upload a photo. Then I activated NextGEN Gallery Media Library Addon, and I was able to add a photo.
I then tried to activate NextGEN Gallery Search, and I got a white screen.
I then tried to activate WP NextGen Gallery Search, and I got a white screen.
I then tried to activate Yoast SEO, and I got a white screen.
I then tried to activate WP Sitemap Page, and I got a white screen.
I then quit trying and deactivated NextGEN Gallery Media Library Addon. I then tried to activate WP Sitemap Page, and it activated.
I then tried to activate the Templatic Directory2 template (where i was unable to upload photos before), and it activated. I then tried uploading a photo, and I was successful.
Looks like the problem could be the NextGEN Gallery Media Library Addon by Jagged Edge Media.
So, it looks like I have solved my problem. I will now test adding a photo after I activate each plugin to see if I find other problems.
Thank you.