CAPT OF ACR LGT ACFT RETURNED TO LAND AFTER HAVING A MALFUNCTION OF THE ACFT WING LEADING EDGE SLAT.

Narrative

AFTER TKOF AND NORMAL INITIAL CLB TO 10000 FT WE BEGAN AN ACCELERATION. AT APPROX 11000 FT; WE GOT A MASTER WARNING AURAL AND MASTER WARNING LIGHT. A MESSAGE ALSO APPEARED ON EICAS (LEADING EDGE SLAT ASYMMETRY) AND A 'LEADING EDGE' WARNING ILLUMINATED. WE ACTIVATED THE ALTERNATE LEADING EDGE SWITCH ONCE BUT GOT NO CHANGE. FLAPS AND SLATS INDICATOR SHOWED FULL UP. THE ACFT WAS SLOWED TO 240 KTS AND THE BOOK ABNORMAL PROC FOR THAT PROB WAS ACCOMPLISHED. THE WARNING LIGHT AND EICAS MESSAGE REMAINED. AFTER TALKING WITH COMPANY DISPATCHER AND COMPANY MAINT COORDINATOR; A DECISION WAS MADE TO RETURN TO POINT OF ORIGIN. I ELECTED TO NOT DECLARE AN EMER BECAUSE WE WERE OFFERED A LONG CLEAN DRY RWY (9000 FT). THE PROC CALLS FOR AN ALTERNATE (ELECT) EXTENSION OF THE FLAPS WITH THE SLATS RETRACTED AND A THRESHOLD SPD OF VREF (30) PLUS 30. I CONSIDERED THIS TO NOT BE A PROB ON A 9000 FT DRY RWY. A NORMAL (THOUGH A BIT FASTER) APCH WAS MADE FOLLOWED BY A NORMAL TOUCHDOWN AND ROLLOUT. REVERSERS WERE USED TO 60 KTS AND NORMAL BRAKING WAS APPLIED. NO OTHER PROB WAS ENCOUNTERED CONCERNING THE FLT CTL PROB; BUT; AFTER LNDG; WE REALIZED WE HAD NOT SET THE CABIN TO THE NEW ARPT ELEVATION. ON THIS ACFT THE PRESSURIZATION IS FULLY AUTO; AND THE ONLY THING REQUIRED IS TO SET THE LNDG FIELD ELEVATION DURING PREFLT. A DOUBLECHK OF THIS IS ON THE DSCNT CHKLIST. WE EITHER MISSED SETTING IT OR MISREAD THE SCALE DURING THE DSCNT CHKLIST. THEREFORE; AFTER LNDG; THE CABIN HAD TO ADJUST TO DEP FIELD ELEVATION. MAINT LATER INFORMED ME THAT THE SLAT PROB WAS CAUSED BY A BROKEN SLAT ACTUATOR.