B757-200 FLT CREW HAS TRACK DEV ON SEAVU ARR TO LAX.

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ON SEAVU1 STAR TO LAX AT 17000 FT; WE HAD A FREQ CHANGE TO SECOND SOCAL CTLR WHO GAVE US A NEW CLRNC TO DSND VIA SEAVU1 STAR TO RWY 24R. WE HAD PLANNED AND INSTALLED THE SEAVU1 TO RWY 25R INITIALLY; THE EXPECTED RWY AND APCH COMBINATION. INSIDE KONZL AT 17000 FT; I RESELECTED THE SEAVU1 ARR WITH THE RWY 24R LINK AND EXECUTED IT. THE FO REVIEWED IT AND SAID IT DIDN'T LOOK RIGHT DUE TO TOO MANY DISCONTINUITIES. I RESELECTED THE ARR AND RWY COMBINATION; BUT ADDED THE PALAC TRANSITION WHICH ELIMINATED ONE OF THE DISCONTINUITIES AND CONNECTED US TO THE RWY; WHICH WAS OUR CLRNC. AT THIS TIME WE GOT A SPD REDUCTION AND THE FO ASKED FOR ME TO SET THE NEXT XING RESTR SO WE COULD START. THE NEXT INTXN WITH XING RESTR WAS DIXXN ON THE FMS; SO I SET 12000 FT. I ALSO CLOSED THE DISCONTINUITY BTWN OUR POS AND DIXXN. IN LNAV MODE WE TURNED TOWARD DIXXN AND STARTED DOWN KNOWING WE WERE ABOVE THE XING RESTR AT CATAW OF 14000 FT OR ABOVE. SHORTLY ATC ADVISED THAT WE WERE N OF COURSE. I LOOKED AGAIN AT THE CHART AND THE FMS AND REALIZED THAT SEAVU INTXN WAS NOT SHOWING AND THAT WE SHOULD HAVE GONE OVER IT BEFORE TURING TO DIXXN. WE MANUALLY LOADED SEAVU THEN DIXXN AND EXECUTED AND CORRECTED COURSE. WE CONTINUED THE ARR AND APCH TO LAX NORMALLY. THERE APPEARED TO US THAT THERE WAS NO TFC CONCERN SINCE ALL TFC WAS SHOWING S OF OUR COURSE. FO AND I AGREED THAT SELECTING SEAVU1 ARR SHOULD HAVE AT LEAST HAD US XING SEAVU INTXN AND THAT IT SHOULD NOT HAVE DROPPED OUT. WE HAVE HAD THIS CHANGE OF CLRNC MULTIPLE TIMES GOING INTO LAX WITHOUT SIMILAR PROBS. WE HAD CHANGED FMS DATABASE ON NOV/XA/06; JUST PRIOR TO THIS FLT AND WONDERED IF THIS MAY HAVE BEEN A DATABASE ERROR. COMPLICATING THE SITUATION IS THAT THIS IS A VERY BUSY TIME; CHANGING ARRS AND RWYS; GETTING A SPD REDUCTION; SELECTING NEXT XING RESTR. WE HAD ALL FLT MGMNT AIDS ENGAGED AND HAD AGREED THAT 1 PERSON WOULD REMAIN LOOKING OUTSIDE DUE TO HIGH TFC AREAS AND ONE WOULD DO INSIDE WORK.