yes, It works after turning on identity.
it is safe to turning on the identity on StateLogId because single server don't use this table.
only web farm model will use this table to save sessions in this table.
Step 1: Turn on identity
You can manually add identity to StateLogId column
If you use SQL Script:
ALTER TABLE CuteChatTempStateLog DROP COLUMN StateLogId
ALTER TABLE CuteChatTempStateLog ADD StateLogId INT IDENTITY(1,1)
Step 2: Modify configuration (web.config)
<add key="CuteChat.MultipleServerMode" value="true" />
No need to shut down production server.
Many thanks to Adam.