Symptoms
A user's AD account is locked out when attempting to access any Sharepoint site with K2 integration.
Diagnoses
Your password may have been cached for K2 single sign on. Perhaps there was an AD password change, but the cached password had not been updated.
http://help.k2.com/onlinehelp/k2blackpearl/ICG/current/webframe.html_Credentials_Delegation_-_Single_Sign_On.html
Resolution
To clear this cached credential:
a. Log into K2 Workspace as this account
b. K2 Workspace> User Settings > Select your account with the 'K2' Label and perform the 'Clear Cached Password' option