[vishnu]

What it means is that what was supposed to be in the lookaside buffer wasn't there, it "missed." Obviously, that's not supposed to happen, thus the exception is thrown. When an exception is thrown, the processor unwinds the stack with the assumption that there will be code somewhere up the chain that will be able to handle the exception. In this case, that didn't happen. Unfortunately, exception handling is a criminally neglected component of software engineering.