I've installed the shopp plugin sucessfully with my wp 2.9.1 + atahualpa 3.4.4 but when I try and activate it I get a server 500 error message and it fails to activate.
I have run the shopp compatibility plugin, and it gave me the all clear to install shopp with my hosting package.
I am in contact the shopp support guys, and they have responded and are looking into it (this alone is a big improvement on wp e-commerce!). But I was wondering if anyone else here has encountered this problem and know of a fix?