Illegal kernel in adjoin pvar

edit

I tried running a seemingly simple script involving a Fourier transform in a sage notebook

var('A, x, delta, k, dx, t, v, xi')
temp = A*exp(-(x/delta)^2)
temp = integral(temp*exp(-I*k*x),(x,-oo,oo)).simplify()
(delta>0).assume()
(k>0).assume()
(dx>0).assume()
(xi<1).assume()
temp = temp*exp(-I*k*t*v)*exp(-(k^2)*t*v*dx*(1-xi)/2)
temp = integral(temp*exp(I*k*x)/(2*pi),(k,-oo,oo))

and I got the following error message

Condition of type: SIMPLE-CONDITION
Illegal kernel in `adjoin-pvar'
Available restarts:

1. (CONTINUE) Return from BREAK.

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Any idea what's going on?