Hello, I have run into a problem with gluNurbs that I would appreciate some help with. I am attempting to render trimmed NURBS surfaces read from an IGES file. The first few surfaces seem to render OK, but after some number, say N, I start getting a GL_STACK_OVERFLOW error with the call to gluEndSurface. If I render any single trimmed surface, it works fine, so I don't think its the NURBS data. Also, if I render just the untrimmed surface, everything is fine, which points to something in the trimming code. I've checked the depth of the modelview, projection, and texture matrix stacks before and after the glEndSurface call, and they are all what I expect them to be (1 or 2), so the error must be thrown by something in the glu nurbs tesselator. I've searched through the glu code, but haven't found anywhere that the matrix stacks are manipulated, or where GL_STACK_OVERFLOW is thrown, though I did see where it is included in libutil/error.cc If anyone could shed some light on what might be going on, I'd appreciate it. Additional data: Problem seen with GLU libraries shipped with Ubuntu 9.04 and RHEL 5.4 (not sure of versions) Nvidia drivers & core OpenGL pyOpenGL 3.0/3.1 All surfaces and trim curves are non-rational BSplines I'm rendering using object space sampling, but have same error with default pixel sampling Onset of error seems to depend on sampling size, but once one surface has a problem, all following surfaces do. Thanks