AOL stock is down 4% or so today – and it hit a 52-week low of $17.62 earlier this morning.

Earlier this week, AOL CEO Tim Armstrong fired ad sales boss Jeff Levick. Maybe that sent the wrong signal to institutional buyers?

(Tim to Jeff: "The numbers are in…and you're fired.")

If AOL's display advertising sales do disappoint this quarter it will actually be something of a surprise.

They actually grew some last quarter, and one close company watcher tells us Project Devil, AOL's big ad unit, is very popular with agencies and their clients.

"Everyone I speak with are buying more, and most wouldn't touch it in the beginning of the year," says this source.

Big picture, AOL's problem is that even if it does build a decent brand advertising business through Huffington Post and Patch (ha), that business probably won't ever be as big as the subscription business that still accounts for most of the company's profits and market capitalization.

When even success is failure, the road gets really tough.