Symptoms

This happen when there is same email accounts maintained at different account. Eg:- K2:DenallixAnthony and K2SQL:Anthony is sharing the same email account "Anthony@denallix.com".

When Anthony try to action the task via SmartAction, there will be this warning from console indicating that there are multiple accounts maintained at different Identities.
 

Diagnoses

Checked the AllowAmbiguity key in K2HostServer.exe.config and it was turned to false.
 

Resolution

This was resolved after we enabled the "AllowAmbiguity" tag followed by Blackpearl service restart. When that key was enabled, the following logic would apply:-
1) Get all the users under all the labels which have the incoming email address
3) Sort the returned list of users according to their label alphabetically
4) Place the default label first in the list
5) Attempt to action the worklist item using the users in the list in order

Refer to this KB for more details:-
http://help.k2.com/onlinehelp/K2blackpearl/UserGuide/current/webframe.html_K2_SmartActions_Email_Security.html