A couple of issues:
Since you don't specify which version of Fortran you're using, I think what is happening is that you cannot mix the 2 and 3 argument forms of getarg. This is likely to be one problem.
The second problem may be that getarg's two integer arguments, input and status, are 2-byte integers. I believe CVF, by default, uses 4-byte integers, so there may be an alignment problem.
The routine should compile if it's syntactically correct; unless the compiler has access to interface information, it cannot determine if the argument list in you code is the same as the argument list that getarg is expecting; call getarg(), call getarg(input, arg), and call getarg(arg, input) are all syntactically correct, so the compiler will be happy. After all, you may have written a routine named 'getarg' or be using one named 'getarg' from a 3d party library.
So my suggestions are:
Add the appropriate "USE" statement (USE DFLIB for CVF 6.6)
Explicity declare input and status to be integer(2).
Unless you've got one-byte command line arguments, declare arg to something generous, like character*256. Do not declare it as character arg(256). These are not equivalent!
Hand check your code to make sure the interfaces are right.
