Attach sparsebundle fails - hdiutil not working for me

Thanks for reading this post. I've seen so many solutions that involve something like:

"hdiutil attach -readwrite -nomount -noverify -noautofsck /Volumes/Data/mbp.sparsebundle"

but I always get "hdiutil: attach failed - not recognized"

The 1.72 TB file resides on a 2nd generation Time Capsule. My laptop disk died and I believe the errors in the disk must have continued to the Time Machine backup. I have read so many posts across the web which all involve some form of the terminal command line above.

I can't mount the image. I can't open it in disk utilities but I can open the contents of the file and see the "bands". I don't wish to restore, only recover certain files.

Is there something I'm missing?

Thanks,

ed