Make backup of your skype database "main.db" located in C:\Users\PROFILE NAME\AppData\Roaming\Skype\SKYPE LOGIN ID
Use SQLLite and open the database
( more info about SQLLight :http://sqlitebrowser.sourceforge.net/index.html)
( Download http://sourceforge.net/projects/sqlitebrowser/)
Run a new query as follows :
look existing data
Select * FROM "Messages"where dialog_partner = "skype name"
Delete Data
DELETE FROM "Messages"where dialog_partner = "skype name"
(skype name = skype.name )
save the SQLLite DB
And Restart the Skype
