Try doing a 'save as' and save the file under a new name. If this doesn't work, you may have too many objects in your scene (too high poly count). try deleating one at a time and then save. Also, if you have imported mats that are too high resolution this will cause a problem too. try downsizing any imported photo mats by reducing the dimensions/dpi size and reimport into your scene. Also, and I realize that this is too late to mention but it is helpful for future renders, you should get into the habit of hitting the save button every 5/10 minutes. This way, when you run into a problem in Bryce with saving a file, you won't lose too much of your work from the last save.