The "set of all sets" would have to contain itself, along with all the other possible sets.
For ease of writing, let's pretend that there are only three sets: X, Y, and Z.
Now the set of all sets is this set: {X, Y, Z}. Let's call this set S so that S = {X, Y, Z}.
But, S doesn't contain set S. Now the set of all sets is {S, X, Y, Z}.
Let's call this set T so that T = {S, X, Y, Z}.
But T doesn't contain set T. Etc. Etc. Etc. Do you see the problem?