Scheduler not installed; ERROR: 'str' object has no attribute 'decode'

[4037B]

Hi,
I would really appreciate some help/suggestions on how to resolve an error that occurred during dask-ec2 up command.
my command is ask-ec2 up --keyname iap_test_2 --keypair .ssh/iap_test_2.pem --region-name us-east-2 --ami ami-167f5773 --tags iap_test_2:dp --count 2 --volume-size 8 --type t2.micro --nprocs 1

and my terminal shows:

DEBUG: Searching for default VPC
DEBUG: Default VPC found - Using VPC ID: vpc-71f34c18
DEBUG: Searching for default subnet in VPC vpc-71f34c18
DEBUG: Default subnet found - Using Subnet ID: subnet-8e4196f5
Launching nodes
DEBUG: Checking that keyname 'iap_test_2' exists on EC2
DEBUG: Checking that security group 'dask-ec2-default' exists on EC2
DEBUG: Getting all security groups and filtering by VPC ID vpc-71f34c18 and name dask-ec2-default
DEBUG: Found Security groups: [ec2.SecurityGroup(id='sg-aa58a5c1')]
DEBUG: Getting all security groups and filtering by VPC ID vpc-71f34c18 and name dask-ec2-default
DEBUG: Found Security groups: [ec2.SecurityGroup(id='sg-aa58a5c1')]
DEBUG: Creating 2 instances on EC2
DEBUG: Tagging instance 'i-03619720e7d0979e7'
DEBUG: Tagging instance 'i-0d9f1ef72b8caa468'
Checking SSH connection to nodes
DEBUG: Checking ssh connection for 18.218.223.75
DEBUG: Attempt 1/10 of function 'check_ssh' failed
DEBUG: Checking ssh connection for 18.218.223.75
DEBUG: Running command bash -c 'ls' on '18.218.223.75'
DEBUG: Checking ssh connection for 13.58.177.156
DEBUG: Running command bash -c 'ls' on '13.58.177.156'
+------------------+-----------+
| Node IP | SSH check |
+==================+===========+
| 18.218.223.75:22 | True |
| 13.58.177.156:22 | True |
+------------------+-----------+
Bootstrapping salt master
DEBUG: Running command sudo -S bash -c 'curl -sS -L https://bootstrap.saltstack.com | sh -s -- -d -X -M -N stable' on '18.218.223.75'
DEBUG: Attempt 1/3 of function '__install_salt_master' failed
DEBUG: Running command sudo -S bash -c 'curl -sS -L https://bootstrap.saltstack.com | sh -s -- -d -X -M -N stable' on '18.218.223.75'
DEBUG: Attempt 2/3 of function '__install_salt_master' failed
DEBUG: Running command sudo -S bash -c 'curl -sS -L https://bootstrap.saltstack.com | sh -s -- -d -X -M -N stable' on '18.218.223.75'
DEBUG: Attempt 3/3 of function '__install_salt_master' failed
ERROR: 'str' object has no attribute 'decode'
Couldn't bootstrap salt-master. Error is above (maybe try again)

running
`import distributed
print(distributed.version)

import dask
print(dask.version)`

gives

1.20.2
0.16.1

I am using python 3.6

Thank you so much in advance!