Meaning of "DAE appears to be of index greater than 1"?

I am having some trouble getting ODE15s to run on a 10x10 system, continuing to receive the error "This DAE appears to be of index greater than 1." I do not think this is the case though. Internet research tells me that normally initial conditions are the problem, but I am defining my IC's for the 2 algebraic equations such that they agree with equations 2 and 3.

The system mass matrix is:

1 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 1 0 0 0 0 0 0

0 0 -1 0 0 0 1 0 0 0

0 -1 0 0 0 0 0 0 1 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 1 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 1

The right hand side is: (note, I am using the syntax y(x) instead of y(t) here)

[a(x)

b(x) - y2(x)

c(x) - y3(x)

d(x)

e(x)

f(x)

0

y7(x)

0

y9(x)],

Where a(x), b(x), etc. are all defined functions of x.

Any help would be greatly appreciated. I can post the code if necessary but first I am wondering if I am doing something fundamentally wrong.