Symptoms

After upgrade of K2 BlackPearl environment to a newer version any or some SmartObjects which referenced SharePoint via the SharePoint Service V2 are failing with a HTTP Header SOAP Action error:

Server did not recognize the value of HTTP Header SOAPAction:
SourceCode.Sahrepoint.WebServices/GetListItemsFromListNamebyQueryWithFilter.
 

Diagnoses

This error usually indicates a difference in K2 component version installed on the K2 Server(s) and Sharepoint server(s).
Right question to ask here is whether when upgrading the K2 Server(s) to a newer version, was the K2 blackpearl installer was also ran on all Sharepoint server(s) WFEs to upgrade the K2 for Sharepoint 2010 components to the same version of K2?
Next, after the upgrade of the K2 for Sharepoint 2010 components on the Sharepoint server(s), the "K2 for Sharepoint Configuration Wizard" will need to be run from the Central Administration server to upgrade the solutions, update, and also you have to re-activate the K2 features and Configurations to the necessary site collections.
 

Keep in mind that in case of any patches/coldfix were applied in your environment they should be applied consistently across all yor servers to avoid the same version mismatch issues. I.e. if your patch/coldfix affects SharePoint Service V2 it is have to be applied both on K2 server(s) and on SharePoint WFEs otherwise you may run into similar errors.

Resolution

Verify that you do not have version mismatch between K2 components installed on K2 blackpearl server and your SharePoint WFEs.