Extending Bauer's corollary to fractional derivatives

We comment on the method of Dreisigmeyer and Young (2003 J. Phys. A: Math. Gen. 36 8297) to model nonconservative systems with fractional derivatives. It was previously hoped that using fractional derivatives in an action would allow us to derive a single retarded equation of motion using a variational principle. It is proven that, under certain reasonable assumptions, the method of Dreisigmeyer and Young fails.