When I try to do the friendship/romance/erotism topics, it works well at first. Then after awhile, I talk to them again, and it says I don't have the privilege to do that or something.
This is actually a common problem. From time to time I have that message appear and my character and her significant other have been married for quite some time (and she never used the prostitution add-on. Just the base mod.) Disposition doesn't have anything to do with it. My character's husband is always at 100% toward her.
All you need to do is close the dialog box then open it again. You should be able to proceed as normal. On rare occasions you'll get the "privileged information" message a second time, but as I said, that is very rare. 99% of the time just closing the dialog box and opening it again works for me.