Unfortunately, by painting over the filenames you have covered up important information - I can't be sure about your precise steps.
Also: besides fixed vs dynamic, another common reason for this error is when the new size you selected is smaller than the old size, but you haven't told me what the old size is so I don't know if this applies.
Why don't you try resizing with
CloneVDI? It has a GUI interface, it should be easier. It also supports fixed disks as input - though the output is always dynamic of course.