This is the command:

sudo sfdisk -d /dev/sda | sfdisk --force /dev/sdb

It fails because permission is denied and the entire error message looks like this:

/dev/sdb: Permission denied

sfdisk: cannot open /dev/sdb read-write

Warning: extended partition does not start at a cylinder boundary.

DOS and Linux will interpret the contents differently.

I already tried formatting the sdb drive with disk utility or even removing the format and leaving it as unallocated space but nothing succeeded.
How should I execute it?
Thank you :)

PS: Ubuntu 12.04 are used