[Help-glpk] lpx_integer problem "optiomal solution of LP relaxation"

[Joonas Timo Taavetti Kekoni]

I have a problem that is solved  ok  with lpx_simplex.

I changing it into a MIP problem by doing
1st     lpx_set_class( LPX_MIP )
2nd     lpx_set_col_kind  LPX_IV or LPX_CV for all vars.
4rd     lpx_integer to the LPX object.

I get:
>lpx_integer: optimal solution of LP relaxation required
204 (==LPX_E_FAULT)

What should I do to get the problem solved?

What is "optimal solution of LP relaxation",
and how should I do it? I found it also from the docs, but it
is not explained there.

Should I solve the problem first as LP problem and only after that try
it as MIP problem?

Or does the error message mean that there is no integer solution to the
problem?

BTW:
        I am using glpk 4.1 and java maping.
        I have not used presolve or other rutines like that not
        changed any defaults.