Singular

Does any body knows what is wrong here:
ring c7 = (0,e),(x, y_(1..14)), lp;
> minpoly = rootofUnity(7);
> c7;
// characteristic : 0
// 1 parameter : e
// minpoly : (e^6+e^5+e^4+e^3+e^2+e+1)
// number of vars : 15
// block 1 : ordering lp
// : names x y_(1) y_(2) y_(3) y_(4) y_(5) y_(6) y_(7) y_(8) y_(9) y_(10) y_(11) y_(12) y_(13) y_(14)
// block 2 : ordering C
> poly f = (x13-e)/(x-(1/e));
def R91 = Roots(f);
// ** redefining roots **
? identifier roots not found in ROR
? error occurred in zeroset.lib::Roots line 127: ` list roots = imap(ROR, roots);`
? leaving zeroset.lib::Roots
skipping text from `;` error at token `)`