Symptoms  

After upgrading from 4.6.8 to 4.6.10 the following error is thrown:

System.Exception: Error occurred when Get WorkItems. ---> System.Exception: Method could not be resolved!
at SourceCode.Workflow.Management.WorkflowManagementServer.GetWorklistItems(String whereClause, String orderByClause, String paramList, Dictionary`2 ParamDic, Int32 PageIndex, Int32 Maxpage)
at SourceCode.Workflow.Management.WorkflowManagementServer.GetWorklistItems(WorklistCriteriaFilter filter)
 

Resolution

Referencing the below community post - Typically, the "Method could not be resolved!" error is due to a version mismatch between servers. Double check via Control Panel -> Programs and Features on all K2 related servers that the versions match.

Please ensure that all K2 products have the same version, this includes (K2 BlackPearl, K2 SmartForms, K2 SmartForms Control Pack, K2 for SharePoint), should there be a one that is not the same version then you will need to update them as well.

Community Post:
http://community.k2.com/t5/K2-blackpearl/Smartobject-throws-quot-Method-could-not-be-resolved-quot/td-p/73476