As an alternative to named ranges, consider that
=AVERAGE(A2,A4,A6,A8,A10,A12,A14,A16,A18,A20,A22,A24,A26,A28,A30,
A32,A34,A36,A38,A40,A42,A44,A46,A48,A50,A52,A54,A56,A58,A60,
A62,A64,A66,A68,A70,A72,A74,A76,A78,A80,A82,A84,A86,A88,A90,
A92,A94,A96,A98,A100)
refers to 50 discontinuous cells via 50 arguments, and so is not permitted.
=AVERAGE((A2,A4,A6,A8,A10,A12,A14,A16,A18,A20,A22,A24,A26,A28,A30,
A32,A34,A36,A38,A40,A42,A44,A46,A48,A50,A52,A54,A56,A58,A60,
A62,A64,A66,A68,A70,A72,A74,A76,A78,A80,A82,A84,A86,A88,A90,
A92,A94,A96,A98,A100))
refers to 100 discontinuous cells via 1 argument, and so works without
error.
Jerry