Most XSI illumination models (phong, blinn, anistropic, etc...) all have a "frost" parameter for transparency. So if you're having problems with such as simple scene, try XSI.
Just because you have a problem with mental ray does not automatically mean it mental ray's fault. Sometimes it's a poorly written shader that does the whole thing in. When a shader is active, it's responsible for everything it touches, mental can only stand off the side and watch until the shader is done or until the shader requests help. Think of a shader as an independent program running inside of mental ray. In XSI, this barrier has been decoupled somewhat to blend all the pieces together a bit more homogenously. Also, sometimes the problem is the interface between mental ray and SI3D. The more you shift your data to one side or the other, the fewer of these issues you'll encounter.
The stability of the frost shader is dependent on how many samples you set it at. The higher the samples, the more memory you need and the longer it takes as it has to acquire more information about the scene. In such an interval, a bad piece of data may be encountered which is why maybe your scene hangs on frame 20. Try rendering from the command line to see if that helps. It may be a memory issue and by rendering command line you free up a bunch of resources normally needed to support the SI3D interface. When I say command line, I mean via mi files with ray2.exe, not soft -R.
Matt
Matt Lind
Animator / Technical Director
Softimage certified instructor:
Softimage|3D
Softimage|XSI
speye_21@hotmail.com