Take a look at the Cohesive Networks Documentation site for all information related to your VNS3 Network Platform (VNS3, VNS3:ms, and the CNVPN client). Specific VNS3 Troubleshooting Documentation is available on the Documentation Site.
IPsec troubleshooting can typically be resolved by ensureing both sides of a tunnel are using exactly the same parameters. Cohesive Networks always recommends filling out the VNS3 Support Checklist Spreadsheet or similar when planing and negotiating IPsec tunnels.