pbuffers and 3d textures

The answer to this may be obvious but I can’t find it out “there” anywhere. :confused: Is it possible to access 3d textures when rendering in a pbuffer?
Basically I want to draw a quad that fills the pbuffer and have it textured w/ a slice of my 3d texture. I have a cg fragment program that does a basic texture fetch:
color = tex3D(texture,texCoord);

In my display routine I basically activate my pbuffer, draw a quad w/ texturing disabled(so my cg program does the work) and then specify the texCoords and verts for my quad. However, after the glEnd() call, I get an error: Invalid Operation. :mad:

The only examples I’ve seen using pbuffers use 2d textures so I’m thinking that is my problem. But maybe I need to specify certain attributes when I allocate my pbuffer or something else I may be over looking .
Thanks in advance for any help.