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var edit_rec=nlapiEditCurrentLineItemSubrecord('item', 'inventorydetail');
										    				  edit_rec.selectLineItem("inventoryassignment", x);
										    				  edit_rec.setCurrentLineItemValue('binnumber', searchresult);
										    				  edit_rec.commitLineItem("inventoryassignment");

it looks like you're missing your sublist argument in "setCurrentLineItemValue"

try setCurrentLineItemValue('inventoryassignment', 'binnumber', searchresult);