Unable to connect to remote server - Laravel 4.1

Question

I want to execute some commands in a remote server using SSH. This is my configuration :

'connections' => [
'production' => [
    'host'      => '172.55.81.20',
    'username'  => 'user',
    'password'  => '',
    'key'       => 'C:\cygwin64\home\oqannouf\.ssh\id_rsa'
],]

I tried this SSH::into('production')->run(['ls']);
but i get the following error:
Unable to connect to remote server
with no additional informations explaining why it doesn't work.

Note:

• the RSA key is correct and i can use it to login to the server using cygwin.
• Even with a correct password it doesn't work.
• I have all the permissions on the folder C:\cygwin64\home\oqannouf.ssh\