On a Windows agent, the StorageCraft or ShadowProtect services might fail to start when invoked, leading to "Backup failed as Backup job was unable to be assigned (500, 401, 403, 404) / Job Assign Failed!" errors.
On investigation of the Windows Event Logs, an error similar to the following is observed:
Log Name: System Source: Win32k Date: 24-12-2013 20:51:59 Event ID: 243 Task Category: None Level: Warning Keywords: Classic User: N/A Computer: Description: A desktop heap allocation failed.
"Every desktop object on the system has a desktop heap associated with it. The desktop object uses the heap to store menus, hooks, strings, and windows. The system allocates desktop heap from a system-wide 48-MB buffer. In addition to desktop heaps, printer, and font drivers also use this buffer.
Desktops are associated with window stations. A window station can contain zero or more desktops. The size of the desktop heap allocated for a desktop associated with a window station can be changed in the following registry value."
After this error occurs, the ShadowSnap agent software can not communicate with Windows correctly.
To correct this error, you will need to increase desktop heap moving forward. This error is a Microsoft error, and Datto is unable to make specific recommendations as to the amount of desktop heap which should be allocated to the protected system.
MSDN: Desktop Heap Overview