=== Job fails to start due to timeout ===

https://www.veeam.com/kb1909

== Challenge ==

In Veeam Backup & Replication, if more than 100 jobs are running simultaneously, and the user attempts to start more jobs, they may fail to start with the following error message:
  Error Job <JobName> cannot be started. SessionId: <UUID>, Timeout: [361 sec]
A Veeam Agent for Microsoft Windows backup job may fail with:
  Managed session <UUID> has failed 
In the Veeam Agent for Microsoft Windows service logs (Svc.VeeamEndpointBackup.log) following errors are found:
  Error Job <JobName> cannot be started. SessionId: <UUID>, Timeout: [361 sec]
  Error Job [Infrastructure update] has failed to start. Timeout expired (6 minutes). SessionId: <UUID>
The following event is found in the System event logs:
<code>
Log Name:      System
Source:        Win32k
Event ID:      243
Task Category: None
Level:         Warning
Keywords:      Classic
User:          N/A
Computer:     
Description:
A desktop heap allocation failed.
</code>

== Cause ==

By default, Veeam services are run as the LocalSystem account. As a result, all processes are started under NT AUTHORITY\SYSTEM context. If the Windows OS is running out of Desktop Heap memory, new processes can't be started. 
== Solution ==

The Desktop Heap size must be increased via a registry modification.

Because this change will affect the desktop heap of all services (also known as non-interactive window stations), do not make the new value larger than necessary.

Run regedit and navigate to
HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\SubSystems
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Find string named "Windows"

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Edit the Value data to change the third "SharedSection" value only.
Do not modify any other values.

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Press OK
Reboot the machine