If you enclose s {2, 4}, (1 - s) {4, 2} within braces, it becomes a 2 by 2 matrix, not a vector. If you want a linear (convex) combination of the vectors {2,4} and {4,2} you should combine them with a plus sign:
Graphics[Table[
Arrow[{{0, 0}, s {2, 4} + (1 - s) {4, 2}}], {s, 0, 1, 0.025}]]
