Need Help

Hello ,
I need to change the following non linear constraint to a linear one .

the constraints are:

for all k = 0 ,1, 2,3 ,4, 10

k+1 = sum over j ( a[k][j] * d[j] )

j = 1,2,3,4


for all k, j a[k][j] is an integer <= 2 and d[j] is an integer <= 60.


both a[k][j] and d[j] are variables , making it a non linear
constraint. Is there a method i can change it to a linear expression.
Cplex gives a error with this constraint.

Thankyou ,
Arush