Could you please describe step by step all actions you did? In your original message you wrote you have two instances – Kentico 6 and Kentico 8. Now, you wrote “I have updated hotfix with latest version 8.” Does it mean you applied hotfix over your Kentico 8 instance, or you also upgraded your original Kentico 6 to Kentico 8 and apply a hotfix over this upgraded instance? Is the site you have issue with the upgraded one? If so, could you please clarify all steps you did during upgrading from Kentico 6 to Kentico 8? Did any issue or error appear during this process? Is there any error or warning in your Event log application?
Thank you in advance for your clarification.