When you are going to update any message in Construct shape which is already constructed, then you will receive this type of error. Like you are receiving msg1 and just after this receive shape, you are going to construct this message once more. In this type of situation, you will receive this type of error.
To resolve this error,create a new message in orchestration view of same type. And use this new message in new message in construct shape. Same problem can occur when you are sending message to .net assembly too. So make sure when you want to update any message, it must be new.