Question: Error, (in unknown) invalid subscript selector

Hello everyone, I use physics package and I input:

with(Physics)

Setup(mathematicalnotation = true)

Coordinates(X)

Setup(tensors = A[mu](X))

PDEtools:-declare(A(X))

PDEtools:-declare(p0(X), pm(X), pp(X), pt(X), Un(X), Ucn(X))

pt := proc (X) options operator, arrow; Matrix(2, 2, [[p0(X), sqrt(2)*pp(X)], [sqrt(2)*pm(X), -p0(X)]]) end proc

U := proc (X) options operator, arrow; Matrix(2, 2, [[1, 0], [0, 1]])+I*pt(X)*(1/f)-pt(X)*pt(X)*((1/2)/f^2) end proc

Ucn := proc (X) options operator, arrow; Matrix(2, 2, [[1, 0], [0, 1]])-I*pt(X)*(1/f)-pt(X) . pt(X)*((1/2)/f^2) end proc

And after that I write:

Trace(-LeviCivita[mu, nu, rho, sigma] . Ucn(X) . ((1/6)*e*A[nu](X)+M5*KroneckerDelta[nu, 0]) . Matrix(2, 2, [[1, 0], [0, 1]]) . Uсn(X) . d_[rho](Un(X)) . Uсn(X) . d_[sigma](Un(X)))

But I get an error:

Error, (in unknown) invalid subscript selector

Thanks for the help.