Open Message In Conversation - Nothing is making it work properly

Hi folks, having a nightmare with Open Message In Conversation. Its partly not working, or when it does, it doesn't include everything that it should be. I have tried all of the listed previous suggestions (re-doing the global index etc...) on this forum. Can you help? When in my inbox: Open Message In Conversation is completely greyed out and does nothing. When in my outbox: It opens the conversation up to the date of that email, but doesn't include any mails that are more recent anymore (ie. the full conversation). When clicking on the most recent sent mail, it only shows my own replies, and the received mail is no longer included in the conversation. This is a recent thing to happen, and incredibly frustrating as it's killing my work flow. If you have any suggestions, I will try them all to bring it back to how it was! Cheers, Lee