bitstream fonts have lots of kern pairs, which exhaust your poor
little tex. You should use some bigger tex, or suppress some of the
kern pairs. You can also ask fontinst to _ignore_ many kern pairs by
\setint{minimumkern}{20} or so, but that would be sad.
BTW, berry's name for American Garamond is bg3, isn't it?
Thierry Bouche, Grenoble.