Justin Carmony has a recent post to his blog about a problem he came across where his exception was being thrown with a line number of zero - cause for some investigation.

Today I ran into a problem where my PHP Application would throw this fatal error: "Fatal error: Exception thrown without a stack frame in Unknown on line 0". Which is so much fun, because it doesn’t have a line number, so I had no direction as to what exactly was causing the problem.

He found a blog post that helped him track down the issue that, as it turns out, with serializing objects into the session and an error in the __sleep method.