I am trying to use "solve" to solve a set of 2 equations defined by using summation function "sum". But I got an error saying "Error, (in sum) summation variable previously assigned, second argument evaluates to 3 = 1 .. 2". 

The Maple code is listed here

restart;
N := 2:
var:= seq(alpha[n], n = 1 .. N):
v(x):=sum(alpha[n]*phi[n](x), n = 1 .. N):
R(x):=diff(v(x), x $ 4) - p/EI:
eqs := seq('int'('R(x)'*phi[n](x), x = 0 .. L) = 0, n = 1 .. N):
for n to N do
    phi[n](x):= sin((2*n - 1)*Pi*x/L):
end do:       
solve({eqs}, {var});
Error, (in sum) summation variable previously assigned, second argument evaluates to 3 = 1 .. 2