An oldie but a goodie: The Case of the 500-Mile Email:
"We're having a problem sending email out of the department."
"What's the problem?" I asked.
"We can't send mail more than 500 miles," the chairman explained.
I choked on my latte. "Come again?"
"We can't send mail farther than 500 miles from here," he repeated. "A little bit more, actually. Call it 520 miles. But no farther."