Parsing an output file and creating two lists with python

How about something that tracks the current computer as a state, and then checks the ERROR message.

Untested code -

list1 = []
list2 = []
with open(file_name, 'r') as reader:
    current_computer = None
    for line in reader:
        if line.startswith('Computer Name: '):
            current_computer = line[len('Computer Name: '):]
        if line.startswith('ERROR: A compatible Trusted Platform Module (TPM) was not detected.'):
            list1.append(current_computer)
        elif line.startswith('ERROR: The TPM is already on.'):
            list2.append(current_computer)

from collections import defaultdict
import re

def get_computer(row, reg=re.compile('Computer Name: (\S+)')):
    m = reg.match(row)
    return m and m.group(1)

def line_starts_with(s):
    return lambda line: line.startswith(s)
found     = line_starts_with('ERROR: The TPM is already on.')
not_found = line_starts_with('ERROR: A compatible Trusted Platform Module (TPM) was not detected.')

def process_states(inf, value_fn, state_fns):
    states_matched = defaultdict(list)
    value = None
    for row in inf:
        nv = value_fn(row)
        if nv:
            value = nv
        else:
            for state_label,state_fn in state_fns.items():
                if state_fn(row):
                    states_matched[state_label].append(value)
                    break
    return states_matched

def main():
    with open('input.log') as inf:
        results = process_states(inf, get_computer, {'found':found, 'not_found':not_found})

if __name__=="__main__":
    main()

then for testing, I ginned up the following:

import StringIO

inf = StringIO.StringIO("""
BitLocker Drive Encryption: Configuration Tool version 6.1.7601
Copyright (C) Microsoft Corporation. All rights reserved.

Computer Name: AAAAA

ERROR: A compatible Trusted Platform Module (TPM) was not detected.
--- 
BitLocker Drive Encryption: Configuration Tool version 6.1.7601
Copyright (C) Microsoft Corporation. All rights reserved.

Computer Name: BBBBBB

ERROR: The TPM is already on.
--- 
BitLocker Drive Encryption: Configuration Tool version 6.1.7601
Copyright (C) Microsoft Corporation. All rights reserved.

Computer Name: CCCCCC

ERROR: The TPM is already on.
--- 
BitLocker Drive Encryption: Configuration Tool version 6.1.7601
Copyright (C) Microsoft Corporation. All rights reserved.

Computer Name: DDDDDDD

ERROR: A compatible Trusted Platform Module (TPM) was not detected.
""")

results = process_states(inf, get_computer, {'found':found, 'not_found':not_found})

which returns

{'found': ['BBBBBB', 'CCCCCC'], 'not_found': ['AAAAA', 'DDDDDDD']}