I have some DAE's (differential - algebraic equations) in notebooks that solved fine in 7/2013. But now I get and the error:

NDSolve::ivres: NDSolve has computed initial values that give a zero residual for the differential-algebraic system, but some components are different from those specified. If you need them to be satisfied, giving initial conditions for all dependent variables and their derivatives is recommended.

===== I can't find any documentation to the error

The equations are ode's + algebraic + some "WhenEvent" statements and one discrete variable also using Method -> {"IndexReduction" -> Automatic}

Any idea what that error message is telling me?