You have a mismatch between your requested parameters for the function and the Acp matrix.
With the function mini.var.capa.ident(n, k, A.Choquet.preorder = Acp), your first parameter is n = 3. The number of columns in your Acp matrix must be 2 x n + 1. Your second parameter k cannot exceed the number of rows in Acp. Thus Acp must be a m x n matrix with m >= 3 rows, and n = 7 columns (not same n as function parameter).
Even when correcting all this, it is quite possible you will receive a new solve error due to the 3x3 size requested. That will look something like: