Hi 

I am sorry for the late reply (it was a long holiday in Korea)

I. rotating bvecs
You're in a wrong directory. In the directory you typed "fdt_rotate" does not contain the ecc log file.

What you should do is.. 

    1. rotate bvec in the original directory
    2. make a new folder "data"
    3. copy the data.nii.gz (eddy corrected one.) into the data directory
    4. copy the rotated bvecs and bvals into the data directory 
    5. copy the nodif_brain_mask into the data directory.
    6. make sure all names are apppropriate (https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/F...)

ii. bedpostx
I think you did not perform dtifit...
please follow https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FDT/UserGuide

Best
Cheol