Its got to be answering to a non-technical manager. I have had particular problems in the past with the 'hands-on, always in the know' types that need to be educated about the full issue before action is taken.<p>Drags out the most simple tasks.
Leaky abstractions - not really the most original answer, but the layers of abstraction away from the machine code allow me to do things in hours that would take months or more.<p>It's also the source of most of my bugs, most of my slowdown, and it's the reason my C:\Windows folder is 13gb.
Not knowing how to code :)<p>Seriously - in my experience the biggest problem a programmer can have is having a manager that doesn't programming/programmers. The long-term effect of that alone is crippling.