Running large complex workflow randomly fails

This problem might be caused by the large number of Types that are created during workflow compilation, for workflows with many local workflow variables. It is more common for workflows with multiple Approval Process actions, as each preconfigured Approval Process Action comes with a large set of local variables, for the different configurable property of the Approval Process.

RESOLUTION:

By installing a CU that includes the February 2011 CU or service Pack 1 which is the ideal solution, SharePoint administrators are able to prevent compilation of workflows whose compilation would affect the performance of the farm. The default value of the property "UserDefinedWorkflowMaximumComplexity" is 7000, but can be changed based on the needs and profile of the SharePoint farm. Try setting this property to a higher value using PowerShell:

$app = get-spwebapplication "[web app url]"
$app.UserDefinedWorkflowMaximumComplexity = 8000
$app.Update()