You should go to:

http://www.renderplus.com/pdf/download.htm

to get the latest version of IRender nXt - HH01a.

(You mention the preview window. That is no longer used in the latest version of IRender nXt - so it is possible you are using IRender V2.0, or an earlier version of IRender nXt)

We have not had any crash reports with this latest version (although it is always possible that we will see some crashes)

If you still get crashes with this version, let us know, and send your model to
http://wiki.renderplus.com/images/d/d3/Support-email.PNG
if you can so we can try it here.

(Usually are crashes are not related to OpenGL settings. They are more likely caused by large models, and with some problems we have been having extracting the data properly for the renderings.)