The reason for the crash is pretty obvious from the log (PC is too busy, too many read locks)... but I thought I would post it anyways just in case there is something of value in it for you.
# See the 'MyDefrag.log' file for information intended for endusers. This is the debug
# logfile. The contents is highly technical and not documented. See the 'Debug' setting
# or the '-d' commandline option to control the level of information in this file.
#
Version: MyDefrag v4.2.3
Date: 2009/10/20 09:52:16
Windows version: v5.1 build 2600 S
Commandline: "C:\Program Files\MyDefrag v4.2.3\MyDefrag.exe"
Working Directory: C:\Program Files\MyDefrag v4.2.3
Userid: 752171
InstallPath = C:\Program Files\MyDefrag v4.2.3\
09:52:16 Analyzing the commandline.
09:52:16 Running script: Settings.MyD
09:52:16 Showing the WhatToDo dialog.
09:53:00 Added 'C:' to the list of CommandlineVolumes.
09:53:00 Selected script = C:\Program Files\MyDefrag v4.2.3\Scripts\DefragmentOnly.MyD
09:53:00 Running script: C:\Program Files\MyDefrag v4.2.3\Scripts\DefragmentOnly.MyD
09:53:00 Processing disk C:
09:53:39 Loading list of unmovable files
09:53:39 Could not open handle for 'C:\Program Files\MyDefrag v4.2.3\MyDefrag.dat': [2] The system cannot find the file specified.
09:53:39 Zone 1 of 1
09:53:39 Defragment
10:31:37 Timeout 1 while waiting to get a read lock for: DrawDiskMap
10:32:37 Timeout 2 while waiting to get a read lock for: DrawDiskMap
10:33:37 Timeout 3 while waiting to get a read lock for: DrawDiskMap
10:34:37 Timeout 4 while waiting to get a read lock for: DrawDiskMap
10:35:37 Timeout 5 while waiting to get a read lock for: DrawDiskMap
10:36:37 Timeout 6 while waiting to get a read lock for: DrawDiskMap
10:37:37 Timeout 7 while waiting to get a read lock for: DrawDiskMap
10:38:37 Timeout 8 while waiting to get a read lock for: DrawDiskMap
10:39:37 Timeout 9 while waiting to get a read lock for: DrawDiskMap
10:40:37 Timeout 10 while waiting to get a read lock for: DrawDiskMap
10:41:37 Timeout 11 while waiting to get a read lock for: DrawDiskMap
10:42:37 Timeout 12 while waiting to get a read lock for: DrawDiskMap
10:43:37 Timeout 13 while waiting to get a read lock for: DrawDiskMap
10:44:37 Timeout 14 while waiting to get a read lock for: DrawDiskMap
10:44:37 Too many timeouts, the computer is too busy. Forcing a crash for debugging purposes.
I have crashed!
Command line: "C:\Program Files\MyDefrag v4.2.3\MyDefrag.exe"
Current context locks:
GetFragments
Exception: ACCESS_VIOLATION (the memory could not be read or written)
1. At line (unknown) in (unknown)
2. At line (unknown) in (unknown)