Nope, it had to have been a glitch. I restarted the game and it worked.
Before, it was never greyed out -- I could research art reference back to back. Now it greys out regardless of the sim's traits.
My sims weren't failing: they weren't completing the task after hours of sitting in front of the computer and exhausting themselves. Now I've seen two failures and I get a note that they failed. This was simply not completing. Really odd.
I'm going to try deleting some save files, since things have been getting slower recently.