The one he posted was definitely a vaild bitcoin address. If he input it wrong into his miner, then solo would have just rejected him entirely.
We don't know if he is actually typing that address without any spaces, or a space in the url itself, or maybe using a wrong password, anyone who seeks support must at least provide
1- A screenshot of the miner status page.
2- A screenshot of the pool settings (you can hide a few digits in the middle).
3- Kernel log.
Without these 3 and without a magic ball, I don't think it's possible to help anyone troubleshoot their miners, some people are too lazy to post these things and all they say is that "my miner isn't showing on the pool" well, good luck.