Sorry for posting like this, can't provide link at the moment. Copy this and then remove the post. There are more chrash reports in the log, but all look similar; it's always Thread 1 that chrashed in function SIT_UnArchive.

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Host Name: franks-ibook
Date/Time: 2006-11-27 21:51:04.620 +0100
OS Version: 10.4.8 (Build 8L127)
Report Version: 4

Command: The Unarchiver
Path: /Applications/Utilities/The Unarchiver.app/Contents/MacOS/The Unarchiver
Parent: WindowServer [7068]

Version: 1.3 (1.3)

PID: 7107
Thread: 1

Exception: EXC_BAD_ACCESS (0x0001)
Codes: KERN_INVALID_ADDRESS (0x0001) at 0xfc707aac

Thread 0:
0 libSystem.B.dylib 0x9000ab48 mach_msg_trap + 8
1 libSystem.B.dylib 0x9000aa9c mach_msg + 60
2 com.apple.CoreFoundation 0x907dcb78 __CFRunLoopRun + 832
3 com.apple.CoreFoundation 0x907dc47c CFRunLoopRunSpecific + 268
4 com.apple.HIToolbox 0x93203740 RunCurrentEventLoopInMode + 264
5 com.apple.HIToolbox 0x93202dd4 ReceiveNextEventCommon + 380
6 com.apple.HIToolbox 0x93202c40 BlockUntilNextEventMatchingListInMode + 96
7 com.apple.AppKit 0x93706ae4 _DPSNextEvent + 384
8 com.apple.AppKit 0x937067a8 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 116
9 com.apple.AppKit 0x93702cec -[NSApplication run] + 472
10 com.apple.AppKit 0x937f387c NSApplicationMain + 452
11 cx.c3.theunarchiver 0x0000292c _start + 760
12 cx.c3.theunarchiver 0x00002630 start + 48

Thread 1 Crashed:
0 de.dstoecker.xadmaster 0x000b3d84 SIT_UnArchive + 6244
1 de.dstoecker.xadmaster 0x0007a888 xadFileUnArcA + 412
2 de.dstoecker.xadmaster 0x0007a9e0 xadFileUnArc + 240
3 de.dstoecker.xadmaster 0x000bf87c -[XADArchive _extractFileEntry:as:] + 252
4 de.dstoecker.xadmaster 0x000bf75c -[XADArchive _extractEntry:as:] + 540
5 de.dstoecker.xadmaster 0x000bf2f8 -[XADArchive extractEntry:to:overrideWritePermissions:] + 352
6 de.dstoecker.xadmaster 0x000bf0b4 -[XADArchive extractEntries:to:] + 316
7 cx.c3.theunarchiver 0x0000428c -[TUArchiveController extract] + 1052
8 com.apple.Foundation 0x9295d194 forkThreadForFunction + 108
9 libSystem.B.dylib 0x9002b508 _pthread_body + 96

Thread 2:
0 libSystem.B.dylib 0x90049ea8 syscall_thread_switch + 8
1 com.apple.Foundation 0x929755d0 +[NSThread sleepUntilDate:] + 152
2 com.apple.AppKit 0x937a3a10 -[NSUIHeartBeat _heartBeatThread:] + 1100
3 com.apple.Foundation 0x9295d194 forkThreadForFunction + 108
4 libSystem.B.dylib 0x9002b508 _pthread_body + 96

Thread 1 crashed with PPC Thread State 64:
srr0: 0x00000000000b3d84 srr1: 0x000000000000d030 vrsave: 0x0000000000000000

cr: 0x44000244          xer: 0x0000000000000000   lr: 0x00000000000b3c78  ctr: 0x0000000000000003
r0: 0x0000000000000000   r1: 0x00000000f00803a0   r2: 0x00000000fc32cfc4   r3: 0x00000000003daae8
r4: 0x00000000003daae8   r5: 0x000000000000000c   r6: 0x0000000000000007   r7: 0x0000000000000100
r8: 0x0000000000403b59   r9: 0x0000000000000001  r10: 0x0000000000401b55  r11: 0x0000000000000003

r12: 0x0000000090003138 r13: 0x000000000189914c r14: 0x000000000189955c r15: 0x000000000183b200
r16: 0x0000000000080000 r17: 0x0000000000000003 r18: 0x0000000000000001 r19: 0x0000000000000013
r20: 0x0000000000077ab3 r21: 0x000000000455e008 r22: 0x00000000044dd008 r23: 0x00000000044dd00b
r24: 0x0000000000000000 r25: 0x000000000077f008 r26: 0x0000000000000000 r27: 0x0000000000000000
r28: 0x0000000001898c08 r29: 0x0000000000000001 r30: 0x000000000183b200 r31: 0x00000000000b2530

Binary Images Description:

0x1000 -     0x9fff cx.c3.theunarchiver 1.3	/Applications/Utilities/The Unarchiver.app/Contents/MacOS/The Unarchiver

0x29000 - 0x3cfff org.mozilla.universalchardet ??? (1.0) /Applications/Utilities/The Unarchiver.app/Contents/Frameworks/UniversalDetector.framework/Versions/A/UniversalDetector
0x72000 - 0xd1fff de.dstoecker.xadmaster ??? (1.3 (libxad 13.0, modified)) /Applications/Utilities/The Unarchiver.app/Contents/Frameworks/XADMaster.framework/Versions/A/XADMaster
0x8fe00000 - 0x8fe51fff dyld 45.3 /usr/lib/dyld...
...
...