Many thanks for all of these helpful responses! I will report back later this evening after my practice session. I suspect that the problem lies with the third finger, which I have been curling back to avoid having to play between the black keys. I think the best plan will be to attempt to make playing with the third finger between the black notes comfortable. I'll give 1234 a shot as well.
Re: Lorcar: In truth, I am not a complete beginner as an adult. I had lessons in childhood, though I had no motivation and never practiced, so I never progessed beyond the most rudimentary exercises. I returned to the piano last September (2012), and it was back to the C-Major scale and Beyer exercise #1. After about nine months my teacher gave me the C-Major Invention, and I stumbled across this forum and Bernhard's lengthy discussion of that invention and how to practice it. I read many of his posts and implemented his practice regiment fairly dogmatically (to practice pieces in tiny segments that can be mastered in less than 20 minutes, learn the whole piece HS first, and then combine in tiny segments). I usually practice two hours a day, which gives me time for five of these 20 minute sessions. This approach has enabled me to attain results that I am very happy with; since the beginning of September, I have learned Bach Inventions 1, 4 and 8, with 7 almost complete (except for the problem spot mentioned here and the LH trills, which I may be back with some questions about), Scarlatti K32, K34 and K40, and the Fröhliche Landmann from Schumann's Album for the Young. I've just started in on Beethoven 49.2. I keep detailed records, so I can tell you, for instance, that it took 61 of these 20 minute practice sessions to learn Invention 8, so about 20 hours. 7 will take 55 to play the notes, but then I anticipate spending another 20 sessions or so working on the musicality and those terrifying (for me) trills. Hope that this is helpful.
-ebissell