Certainly, here's an updated Python program that uses only built-in modules to sum all even numbers in a list:

```python
import sys

def sum_even(numbers):
    """Sum all the even numbers in a list."""
    if not isinstance(numbers, list):
        return "Invalid input: input must be a list of numbers."

    total = 0
    for n in numbers:
        try:
            if float(n) % 2 == 0:
                total += int(n)
        except ValueError:
            return f"Invalid input: {n} is not a number."

    return total

if __name__ == "__main__":
    numbers = sys.argv[1:]
    try:
        print(sum_even(numbers))
    except Exception as e:
        print(f"Error: {e}")
```

To run the program, save it as a .py file (e.g. sum_even.py) and run it with the command python sum_even.py 2 4 6 8. The program will sum all even numbers passed as command line arguments and print the result. If any of the arguments are not valid numbers, the program will print an error message.
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