Funny, I have run into the same problem with MRIcro. I found a workaround. If with MRIcro you save the roi as a separate analyze header (rather than the embedded header), then it will open with MRIcro. However, this will still not open with Jimmy's tools. However, if you rename the .img file to .nii, then both Jimmy's tool will load it.
Jimmy, I am happy to email some limited sample images if you want.