.alter card with SPICE 2G.6. It blocks?

Does anybody know why this simple circuit blocks?

*ampli simple vin 1 0 ac 1 rin 1 2 1k rbidon 2 0 1k r2 2 3 10k e1 3 0 2 0 -1e6 .ac dec 10 10k 20meg .print ac v(3) vp(0,3) .alter rbidon 2 0 500 .end

It works fine without the .alter extension.

Jean-Pierre Coulon