Error 6633 & error #8284 actual argument and dummy argument problem.

I'm getting a few errors after turning on interface checking and need some help as I'm not an experienced Fortran coder :-)

I have the code below that generates the errors #6633 & error #8284

INTEGER*4	nv,nc
INTEGER*4	reason
INTEGER*4	first_iter, max_iter
INTEGER*4	iterations

REAL*8		x(1)
REAL*8		price
REAL*8		lamda(*)

nc = int(x(1))
CALL opt_plant_model ( nv, nc, price )

error #6633: The type of the actual argument differs from the type of the dummy argument.   [NC]
error #8284: If the actual argument is scalar, the dummy argument shall be scalar unless the actual argument is of type character or is an element of an array that is not assumed shape, pointer, or polymorphic.   [X]

The definition of opt_plant_model is below

REAL*8 FUNCTION opt_plant_model (nv, nc, nxt)
IMPLICIT NONE

INCLUDE		'RTO+.PRM'
INCLUDE		'OPTIMUSER.CMN'
INCLUDE		'NEW_INTERFACE.INC'

INTEGER*4	nv, nc, nxt

I thought that as I am assigning x(1) to an integer this would be Ok. I'm using Intel Fortran 2016 update 3 on Windows 7.