Client error: Can't find free port - Error: Timed out requesting agent port for client sessions.

Challenge

Cause

This is caused by the configuration of a Windows server within the Veeam console being set to have a limited number of ports to use.
 
Example:

Solution

To correct this issue go to the properties of the Windows servers that are connected to this issue and check that their port range has enough ports to use.
 
Default: 2500-5000
 
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Step-by-Step Resolution:
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1.  Within the Veeam console click Backup Infrastructure
2.  From the tree on the left expand ‘Managed servers’ and select ‘Microsoft Windows’
3.  Select the server connected to this issue from the list on the Right-Hand side.
4.  From the menu at the top of the screen click Edit Server
5.  On the ‘Credentials’ tab, click Ports…
6.  Within the network settings dialog that opens increase the number of ports in the range.
7.  Click OK
8.  Click Finish to commit the changes.