cartesian_ddg error: "Assertion `files.size() == 1` failed."

I am trying to run the cartesian_ddg protocol (https://www.rosettacommons.org/docs/latest/cartesian-ddG).

I am using the following command:

cartesian_ddg.static.linuxgccrelease \
 -database $ROSETTADB \
 -s min_2b5i-A_0001_clean_0011.pdb \
 –ddg:mut_file themutfile.txt  \
 -ddg:iterations 3 \
 -ddg::cartesian \
 -ddg::dump_pdbs false \
 -bbnbr 1 \
 -fa_max_dis 9.0 \
 -beta_cart

where $ROSETTADB points to the database directory. I am attaching the .pdb and mutfile.

I am getting the following error:

Using mutfile: themutfile.txt
core.init: Rosetta version: rosetta.binary.linux.release-171 r171 2018.09+release.333d996 333d99699777cd6a50d1c1736bacd689f8f1d1df https://www.rosettacommons.org 2018-02-27T09:57:00.705373
core.init: command: cartesian_ddg.static.linuxgccrelease -database /home/cossio/apps/rosetta_bin_linux_2018.09.60072_bundle/main/database -s min_2b5i-A_0001_clean_0011.pdb –ddg:mut_file themutfile.txt -ddg:iterations 3 -ddg::cartesian -ddg::dump_pdbs false -bbnbr 1 -fa_max_dis 9.0 -beta_cart
core.init: 'RNG device' seed mode, using '/dev/urandom', seed=-2080023677 seed_offset=0 real_seed=-2080023677
core.init.random: RandomGenerator:init: Normal mode, seed=-2080023677 RG_type=mt19937

ERROR: Assertion `files.size() == 1` failed.
ERROR:: Exit from: src/basic/options/util.cc line: 49
BACKTRACE:
[0x58ccf98]
[0x5566c4a]
[0x4110dd]
[0x5e12cf4]
[0x61855d]
caught exception 

File: src/basic/options/util.cc:49
[ ERROR ] UtilityExitException
ERROR: Assertion `files.size() == 1` failed.