Question: "invalid subscript selector" given for pdsolver

I've used very similar code before, this time different equations, and for some reason getting the subscript selector thing, which Maple Help claims to have never heard of before.  I've been fiddling around with the code, and NOTHING gets rid of error.  PLEASE HELP!!

> restart;
> Ha := 30;
> c := 1;
> eq1 := Ha*(diff(b(y), y))+diff(u(y), [`$`(y, 2)]) = -1;
> eq2 := Ha*(diff(u(y), y))+diff(b(y), [`$`(y, 2)]) = 0;
> BC1 := eval(u(y), y = -1) = 0;
> BC2 := (D[1](b))(-1)+(eval(b(y), y = -1))/c = 0;
> BC3 := eval(u(y), y = 1) = 0;
> BC4 := (D[1](b))(1)+(eval(b(y), y = 1))/c = 0;
> pds := pdsolve([eq1, eq2], [BC1, BC2, BC3, BC4], numeric, [b(y), u(y)], spacestep = 0.5e-1);
Error, (in pdsolve/numeric/process_PDEs) invalid subscript selector
>
 

For some reason, this is not exactly which I typed, (such as line with $ for double derivative), but close enough.  The error seems to be in the pds line.

What the heck is a subscript selector anyways?

Thanks

-drbones