Error in Authenticating Host Key

We are upgrading servers and have an SFTP protocol script connecting to a site using 5.1.4 which is currently working fine.
However, when we use the same script using 5.9.3 version it gives the following error:
Host key fingerprint is SSH-RSA 1024 55:61.....
Authentication failed

this is the command line we are using to test the connection:
>winscp.com
winscp>option batch abort
winscp>option confirm off


winscp>open sftp://martin:ppppppp@host.com -hostkey="ssh-rsa xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

I cannot find any documentation regarding the 1024 or 2048 options on the ssh-rsa in the host key. Is that the cause of the error?

The new server is a windows server 2012 R2.

Thanks

The host key we are using was supplied by the customer. It is way over 16 characters and does not have any colons.

scates wrote:

The host key we are using was supplied by the customer. It is way over 16 characters and does not have any colons.

Does it start "ssh-rsa 5561", i.e. does it match the key shown by WinSCP (despite a different syntax)?

If it does, just use the format that WinSCP shows.