OK, so this post is for quite the niche audience, but hopefully by writing this I can same some other poor soul some time.
I tried getting a Brother HL-4070CDW color laser printer hooked up to my network using every possible technique--using a USB cable, connecting it directly to my router, using SecureEasySetup, hitting buttons directly on the printer (to manually type in the 32-digit WEP2 key--good times), etc. No matter what I tried, the printer did not work. Well, it sort of worked with SecureEasySetup, but the printer and my router happily negotiated a different key. Sorry guys, but no; I pick the keys. Regardless of what I tried, the printer would not connect to my network wirelessly.
I finally came to the realization that my WEP2 key was simply too long. Of course, no Brother diagnostic message alerted me to this; it happily accepted my longer key. But once I shortened the key to something more reasonable (~10 characters), the printer connected to the network.
This is strange, but true. I didn't fat-finger the longer key, either! During one of the setup procedures I directly copied the key from the router's admin page to the printer setup window. Oh, Brother!