[Xy-pic] Strange error when typesetting a diagram

[HomXY at gmx.de]

Hello,

I'am trying to typeset the following:

$$\xymatrix{&\pi_1(S) \ar[rd]^{\rho}\\
\pi_1(S\cap S'*)\ar@/^/[rr]^{\rho\circ i_{S\cap
S'*}}\ar@/_/[rr]_{\rho'\circ i_{S\cap S'*}}
\ar@{->>}[ru]^{i_{S\cap S'*}}\ar@{->>}[rd]_{i_{S\cap
S'}}&&{Gl_r(C)} \ar@(ur, dr)[]^\kappa\\
&\pi_1(S')\ar[ru]_{\rho '}}$$

The arrow 

\ar@(ur, dr)[]^\kappa

produces an error message. Can you help me?

Runaway argument?
@@\expandafter \edef \xysplineedges@ {\splineedges@ }\global \let \ETC.
! Paragraph ended before \testsplineedges@ was complete.
<to be read again>
                   \par

Thanks

Sönke

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