Thanks for the reply.
I also noticed all the junk in the log from the Distant Objects Enhancements mod. That mod appears to be working fine, unless it has something to do with Scatterer's broken sun flares.
Regarding the issue at hand with KAS, after trying to take out individual mods one at a time (close game, delete mod, restart), I wasn't having any luck, so I gave up for the night. The next day, when I loaded up KSP after a cold boot of the computer, the problem was gone. Attachments and grabs were working fine again. Bizarre... Someone on Facebook suggested it could be an issue using a trackpad versus a mouse. I am playing on a Macbook Pro and sometimes I use the trackpad, sometimes a USB wireless mouse. If I encounter this issue again, I will make a note of more of the circumstances.
This is such a great mod. I would have to completely re-think my KSP career strategy if it were to crap out on me.