it is a know issue that Agents with 1.5 fail, if a license for 2.0 is added.
Veeam Backup and Replication
• Veeam Agent for Windows license added to Veeam Backup and Replication console will cause existing Veeam Endpoint Backup 1.5 jobs to fail. To work around this issue, delete the Beta license file from the console.
But where exactly can the license be removed?