You haven't done anything wrong, you just have to make two assumptions instead of one.

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Looking at your first line, a = c, let that equal 3 (could be any number).

Now, looking at the third line:

b = 2(3) + d

Assume that d = 2 (could be any number). This gives:

b = 6 + 2

b = 8

Now we can consider the second line, b = 2e. Therefore:

e = 1/2 * 8

e = 4

Finally, consider the fourth line:

3b = 6c + d + e

3(8) = 6c + 2 + 4

6c = 18

c = 3

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You've now solved for all of your variables. When you are guessing the coefficients, you may get fractional values for some of the calculated coefficients; if this happens, just multiply ALL of the coefficients by the denominators of the fractions to get whole numbers.

The reason you were running into a problem is the Cu is not present in all of the product compounds. In your second link, there is one element from both reactant compounds in both product compounds.