What SifJar said: discs and going online triggers a "check for IOS'es" routine. This also checks port 249. If the version of any IOS (including 249) is lower than what's on the latest firmware, it'll give you that message.
There is an official IOS249. It contains no code; just has a high number. This is nintendo's anti-homebrew measurement.
Best to block it with priiloader, as whatever got you htat message isn't going to go away.
Oh, and...your flag shows USA...so how come you have 4.3E as firmware? (sure it's not 4.3U?)