How very odd. Well, I did a bit more digging through the code and I have a headache now
1) For the social buy error, the code seemed straight forward enough. The line that it theoretically is barfing on compares the social interactions "Bar" attribute to determine if it is indeed in the "Bar" category. It then looks like, when it assigns this value to the Stack Object, it is 0... which seems to be bad. Either this means that the bar attribute was not properly initialized, the value was reset, or you have some hack that changes this BHAV.
Now, I am not quite sure what an "Error: Reference to tree tree parameter when no parameter exists." error is, but from the message, it appears that it is looking for a parameter that doesn't exist. This might be due to the stack object being 0. This means the "Bar" attribute was 0 for some reason. Unless you have a sneaky hack that changes this BHAV, in which case the code could be totally different. Is the bar that you have a custom made one or a Maxis one? If it's Maxis, then maybe, have you done anything recently that my have reset your game? Otherwise, I don't know why this would happen, unless it's possible to actually have objects with an id that is 0.
Someone with more experience will most likely know better than I, but I thought I'd at least offer some kind of explanation. Even though it's pretty worthless, lol.
2) For the conversations error, I looked through a lot of the code, and it seems that almost any interaction revolving around drinks (including coffee, regular drinks, bar drinks, etc.) make a call to the BHAV 0x7FD46CD0, Instance = 0x26C, Title = Conversation - Do and pass Param 0 as 0. Almost all other references to that bhav that involve conversations, including socials, chatting in bed, in cars, on sofas, etc. pass an actual value, usually the container (that the sim is inside) or whatever is the current stack object.
At first, I suspected that this might be the problem, but since I found that all other drink related references pass 0, and don't seem to generate errors, at least not in my game, then I don't know why this particular problem is giving you an error. Sorry I can't help.
Maybe someone more knowledgeable like twojeffs, Pescado, or jase might be able to take a look.
Ste