You are confusing the "-type" flag (which has to do with the dataset output) with the input image type. to3d tries to auto-detect the input image type. This is failing badly in your case.
I could add a flag to to3d to tell it to skip trying the DICOM image type. But I can't do that today - I'm too busy. If you are reading the typical 8192 byte long 64x64 files from MCW, then you can change the image filename specification from
exp1/exp1\*
to something like
'3D:0:0:64:64:1:exp1/exp1*'
which should force the input image files to be read in the correct way.
bob cox