Name: Rolf Mertig Date: 05/12/13-12:04:04 AM Z
Put
$LimitTo4 = False
before invoking OneLoop.
Alternatively you can use
OneLoopSimplify[den*SP[q, q]^2, q]
and then OneLoop or just do the integrals by hand.
Taking the limit to 4 can be tricky in the Passarino-Veltman scheme and it is easy to do mistakes (by hand or by computer)
Rolf