The sims 2 graphics problem..?

i just bought the new sims 2 ep 'free time' and now the neighbourhood gr (wen in the neighbourhood panel) are flashing purple and the walls are flashing red!!i already have 'nightlife', 'university' and 'ofb' installed before and nothing was flashing before. i dont think its the ram in my comp coz it already happend to me bef. wen i installed glamour life stuff. in instaled glmor life before 'ofb' but there were walls flashing red so i uninstaled it and then i bought ofb and magically the walls werent flashing. now its happening again wit free time and it really annoys me so please help me...but just in case you need it to answer my question, my RAM is 736 (i think) and im using windows XP (home)...please help me..please make your answer easy to understand...10 pnts for the answer which i understand and which actually solves my problem...