Yes, I am using 3D NifTi files, but it did work for some of my subjects. So, I stopped trying the delete images step, and it's now choking on the slice timing correction (usually fails on the 2nd or 3rd participant). I've verified the number of slices, slice acquisition order, and am using the last slice as the reference slice. I'll admit I'm still relatively new to SPM'd preprocessing but it seems that I have everything in order. Any ideas why this might be failing?