DIAGNOSIS Mineral scale (white crusty buildup) and mold are the two main enemies. You don't need the branded cleaner; common household stuff works if you use the right process.
FIX For a descale cycle: Unplug, empty all ice and water. Mix a solution of 2 cups warm water and 1 cup white vinegar. Pour it into the reservoir. Plug in, press and hold the 'Power/Select' button for 3 seconds to start a fill cycle. Let the solution sit in the system for 15-20 minutes, then run a full ice cycle (discard this ice). Finally, run 2-3 cycles with fresh water to flush out any vinegar taste.
IF THAT DIDN'T WORK For mold or slime (common if it's been stored wet), you need to physically scrub. After the vinegar sit, unplug it again, remove the reservoir and ice basket, and wipe down every accessible surface with a soft cloth and mild soap. Pay special attention to the rubber seal around the evaporator housing.
HEADS UP Never use abrasive scrubbers, bleach, or ammonia-based cleaners on the interior plastic or the evaporator plate. It can damage the coating and make ice stick permanently.