A B737-300 CREW HAD TRACK DEV WHILE FLYING THE SKEBR 2 RNAV APCH INTO LAS.

Narrative

DURING DSCNT INTO LAS ON THE SKEBR RNAV 2 ARR; I CHANGED THE ALT IN THE CDU AT MISEN TO FL240 (VICE THE FL240A; WHICH IS NEVER ISSUED) AND VERIFIED THE RTEING AS FAR AS SKEBR. I WAS BEHIND THE PWR CURVE GETTING THE ATIS; SO WENT OFF; RECORDED IT; AND COMPUTED THE LNDG DATA. DISTRED NOW; I FAILED TO RETURN TO THE CDU AND VERIFY THE RTEING AND APCH THE FO HAD SELECTED AFTER SKEBR. AFTER SKEBR; THE ACFT TURNED DIRECT SHAND ON THE ILS RWY 25L. THE CTLR QUICKLY NOTICED WE MISSED THE TURN TO KEPEC AND ISSUED A HDG OF 320 DEGS. WE CHKED THE CDU AND SAW THAT ALL THE FIXES AFTER SKEBR ON THE ARR HAD BEEN SOMEHOW DELETED. WE RE-ENTERED THE ARR IN THE CDU AND RESUMED THE ARR DIRECT IPUMY. FORTUNATELY; THERE WAS NO TFC CONFLICT OR ANY PROB CAUSED BY THE DEV. THE FO; WHO HAD PROGRAMMED THE ARR; WAS UNABLE TO EXPLAIN HOW THE FIXES WERE DELETED. HE RECALLED SETTING UP THE ARR; BUT SAID HE DID NOT LINE-SELECT ANY FIXES THAT WOULD HAVE CAUSED THE DELETION OF THE RNAV FIXES. I TALKED TO A CTLR AT LAS TRACON AFTER THE FLT; AND HE TOLD ME HE HAD SEEN ACFT PROCEED ERRONEOUSLY SKEBR-SHAND PREVIOUSLY. HE ASSURED ME THERE WAS NO CONFLICT AND THAT NO PAPERWORK WOULD BE FILED. LESSON LEARNED -- I ALWAYS VERIFY THE ARR RTEING AND APCH; USUALLY PRIOR TO DSCNT. FROM NOW ON; I WILL NOT ALLOW ANY DISRUPTIONS DURING THIS TASK.