VeeamCDP I/O filter cannot be installed "Error: the operation is not allowed in the current state"

Veeam Support has determined that this issue is most frequently related to a network issue, either DNS resolution failure or neccesary ports were blocked.

DNS Resolution

All servers involved in the I/O Filter installation (i.e., Veeam Backup Server, vCenter, and ESXi hosts) must be able to resolve each other via FQDN.

• Veeam Backup Server ↔ vCenter
• vCenter ↔ ESXi Host(s)
• ESXi Host(s) ↔  Veeam Backup Server

 

Firewall Ports

Ensure any firewall on or between the servers involved in the I/O Filter installation (i.e., Veeam Backup Server, vCenter, and ESXi hosts) have the necessary ports opened to allow communication.

• Required Ports for  Backup Server Incoming Connections
  
• Required Ports for CDP Components
  
  

Other requirements can be found here:

Veeam Backup & Replication User Guide > Continuous Data Protection (CDP) for VMware vSphere > Considerations and Limitations