If you haven't been online lately, there's apparently a in World of Warcraft's Public test realms. According to player testimonies, this particular bug prevents them from properly selecting a realm type (RP, PvP, Normal) at the log-on screen.

The good news is that Hortus has also picked up word on this realm select issue, and has released a solution:

Until it is fixed you can work around this by going into your wowtest/WTF folder and editing your config.wtf file to contain the line:

SET realmName "Arena Tournament"

Aside from this fix, Hortus notes that Blizzard is already looking at the issue. We do note that Hortus' fix isn't a cure-all  - some players report that their realm select problem is still there despite altering their config.wtf file. Those interested in reading up on other possible solutions or updates on this bug may want to visit Hortus' thread at the WoW Forums via the source link.