VPN Site2site with Cisco 3030 unable to connect

Hi,

We're trying to setup a VPN connection between a sophos UTM and Cisco 3030, however within our Sophos logs we're seeing the following errors:

cannot respond to IPsec SA request because no connection is known for 141.50.20.21/32===*********xx:4500[*********]...************:4500[20.10.144.172]===20.0.0.0/8

What's causing this error message? I've double checked both ends but still unable to get a connection.

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