Solution

The behavior is caused by the system running out of so-called desktop heap. Aside from a visible desktop that hosts windows, menus, hooks strings, etc. there are also invisible desktops running under non-interactive Windows stations. These can be thought of as a collection of desktops associated with different processes.

All Rockwell services, and there are a number of them, run under LocalSystem account and that the checkbox Allow Service to Interact with the Desktop is not checked.

As such, Rockwell services require desktop memory from the special section of the desktop heap memory which is limited to 48Mb. The memory from this pool is assigned to the requesting non-interactive services in 512Kb portions by default.

However, the system-wide buffer of 48Mb is also serving other types of third party services:

• Some services may also be running under LocalSystem.
  
• Some may be running under different user account context and with services being allowed to Interact with the Desktop.

On a busy machines, the total desktop heap might be exhausted prematurely, before Rockwell (non-interactive services) has a chance to allocate required desktop heap for their own needs.

Desktop Heap Allocation in the Registry

The size of each desktop heap allocation is controlled by the following registry value:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\SubSystems\Windows

Default Registry Value

The default data for this registry value will look something like the following (all on one line):

%SystemRoot%\system32\csrss.exe
ObjectDirectory=\WindowsSharedSection=1024,3072,512
Windows=On SubSystemType=WindowsServerDll=basesrv,1 ServerDll=winsrv:UserServerDllInitialization,3ServerDll=winsrv:ConServerDllInitialization,2 ProfileControl=OffMaxRequestThreads=16

The solution is to modify the SharedSection value (highlighted in the registry key above) by increasing its third value (highlighted in blue) from 512 to 1024. The modification has been already included in the attached registry key. After the registry is applied, a reboot is mandatory.