Hi Steve,
I apologize for this problem. However, please bear in mind that if one of the process instances in the processing history of an image is incorrect or does not behave correctly, the project cannot include the image in question in a consistent way.
I am working to make the project system more and more robust against
partial errors. For example, in your case the project save operation should have continued excluding the faulty image, instead of aborting completely. The current version of the project functionality is just the first one; we'll improve it much more during the next weeks.
I can't live without the Gaussian Blur
Take a look at the new Convolution tool (Convolution category) working in Gaussian mode.