Symptoms
SP webpart for Work list Item list
Diagnoses
Sequence contains more than one matching element
Error message displayed for workitem list web part on our SP 2010 site
Resolution
Updating the Identity.Claims tables with the correct information and manually added the Claims Type Mappings and Claims type records to match the claim issuer for SharePoint Fixed the issue. After doing this, perforiming an IIS Reset and restarting the K2 Service we were able to load the Worklist Webpart in Sharepoint.