Calling Fortran DLL from VB.net program

[Aliyoos1]

Calling Fortran DLL from VB.Net Program
Hi Everyone,
I need help with the following, I appreciate if someone can help.

I have problem with calling a Fortran DLL from VB.net Program. The VB program provide the GUI while the Fortran DLL does the calculations.

The Fortran DLL opens and reads from data files supplied by the VB program. however, DLL program displays a message that says it can not open the file.

this is VB declaration of the DLL:

DeclareSub WIDTH_SUB Lib"C:\ALI\Namoi_TM\Data\Test\WIDTH_SUB.DLL" (ByVal Rating AsString, ByVal Rating_Len AsInteger, _
ByVal Height AsString, ByVal Height_Len AsInteger, _
ByVal Output AsString, ByVal Output_Len AsInteger)

and here the call statement in the VB program

Call WIDTH_SUB(Rating, Len(Rating), height, Len(height), output, Len(output))

This is where fortran DLL can't pass
SUBROUTINE WIDTH_SUB(RFILE,GFILE,OUTPUT)
IMPLICIT NONE
DLL_EXPORT WIDTH_SUB
CHARACTER(len=*),INTENT(IN)::gfile,rfile,OUTPUT


OPEN(UNIT=100,FILE=rfile,STATUS='old',iostat=ierr)
if(ierr.ne.0)then
write(*,20) trim(rfile)
20 format('Cannot open file ',a,' for input.')
WRITE(*,*)'ierr= ',ierr
go to 9990
end if


the ierr value is 155


and VB error message is "AcccessViolationException was unhandled: Attempted to read or write protected memory."