This happens to me quite frequently as well on two different machines. Both are Ubuntu 9.04, one is 32-bit one is 64-bit. So far this has not happened on my Windows XP machine. All are running Blender 2.49a and Yafaray 0.1.1, using the offical builds (not self-compiled).

So far I have not been able to find any rhyme or reason to it (i.e. no paritcular setting that triggers it) - sometimes I am able to save fine, but more often it just crashes. The output on the console is "Segmentation Fault" and then Yafaray and Blender close instantly. This occurs as soon I click "Save As".

I would be happy to provide any details that will help fix this issue, as it is becoming increasingly frustrating.

For those who don't already know, there are two workarounds:

-Select the AutoSave button in the settings panel (so you don't have to go to the Image/Save As menu)

and/or

-Select the Result To Blender button, which send a copy of the results to Blender's UV image editor and lets you save it from there. This method takes a little longer, but also works.