There are two things wrong here. First, You need parenthesis to enclose the errors:

except (ValueError,IOError) as err:

See a demonstration below:

>>> try:
...     1/0
... except Exception,Exception as e:
  File "<stdin>", line 3
    except Exception,Exception as e:
                                ^
SyntaxError: invalid syntax
>>> try:
...     1/0
... except (Exception, Exception) as e:
...     print e
...
integer division or modulo by zero
>>>

Second, you need a try to go with that except line:

def average():
    try:
        TOTAL_VALUE = 0
        FILE = open("Numbers.txt", 'r')

        for line in FILE:
            AMOUNT = float(line)
            TOTAL_VALUE += AMOUNT
            NUMBERS_AVERAGE = TOTAL_VALUE / AMOUNT
        print("the average of the numbers in 'Numbers.txt' is :",
            format(NUMBERS_AVERAGE, '.2f')) 

        FILE.close()

    except (ValueError,IOError) as err:
        print(err)

except cannot be used without try.

There are two things wrong here. First, You need parenthesis to enclose the errors:

except (ValueError,IOError) as err:

Second, you need a try to go with that except line:

def average():
    try:
        TOTAL_VALUE = 0
        FILE = open("Numbers.txt", 'r')

        for line in FILE:
            AMOUNT = float(line)
            TOTAL_VALUE += AMOUNT
            NUMBERS_AVERAGE = TOTAL_VALUE / AMOUNT
        print("the average of the numbers in 'Numbers.txt' is :",
            format(NUMBERS_AVERAGE, '.2f')) 

        FILE.close()

    except (ValueError,IOError) as err:
        print(err)

except cannot be used without try.

You need parenthesis to enclose the errors:

except (ValueError, IOError) as err:

See a demonstration below:

>>> try:
...     1/0
... except Exception, Exception as e:
  File "<stdin>", line 3
    except Exception, Exception as e:
                             ^
SyntaxError: invalid syntax
>>> try:
...     1/0
... except (Exception, Exception) as e:
...     print e
...
integer division or modulo by zero
>>>

There are two things wrong here. First, You need parenthesis to enclose the errors:

except (ValueError,IOError) as err:

See a demonstration below:

>>> try:
...     1/0
... except Exception,Exception as e:
  File "<stdin>", line 3
    except Exception,Exception as e:
                                ^
SyntaxError: invalid syntax
>>> try:
...     1/0
... except (Exception, Exception) as e:
...     print e
...
integer division or modulo by zero
>>>

Second, you need a try to go with that except line:

def average():
    try:
        TOTAL_VALUE = 0
        FILE = open("Numbers.txt", 'r')

        for line in FILE:
            AMOUNT = float(line)
            TOTAL_VALUE += AMOUNT
            NUMBERS_AVERAGE = TOTAL_VALUE / AMOUNT
        print("the average of the numbers in 'Numbers.txt' is :",
            format(NUMBERS_AVERAGE, '.2f')) 

        FILE.close()

    except (ValueError,IOError) as err:
        print(err)

except cannot be used without try.