Minimize is meant for symbolic computation. Use FindMinimum or NMinimize for numerical calculations.

You will also need to ensure that your function only evaluates with numerical arguments:

• http://support.wolfram.com/kb/12502

You can do this either with a wrapper function (as in the linked article) or by modifying the :Pattern: in the MathLink template.

The tm definition of the function is as follows:

double return_eval_error_p P((double *p, long dp));

:Begin:
:Function:       return_eval_error_p
:Pattern:        ReturnEvalErrorP[p_List]
:Arguments:      {p}
:ArgumentTypes:  {RealList}
:ReturnType:     Real
:End:

:Evaluate: ReturnEvalErrorP::usage = "ReturnEvalErrorP[{}]"