Version 2.40b1, as well as all nightlies after 2.33+(12671) [including the last one, 2.4+(12903)], crash on launch on my system. Prior nightlies still work ok. Here's the report:
Process: Transmission [52088]
Path: /Applications/Transmission.app/Contents/MacOS/Transmission
Identifier: org.m0k.transmission
Version: 2.40b1 (12903)
Code Type: X86-64 (Native)
Parent Process: launchd [331]
Date/Time: 2011-09-21 13:05:37.381 +0200
OS Version: Mac OS X 10.7.1 (11B26)
Report Version: 9
Interval Since Last Report: 225865 sec
Crashes Since Last Report: 4
Per-App Interval Since Last Report: 81 sec
Per-App Crashes Since Last Report: 3
Anonymous UUID: 8BEE7C99-1A1E-44AF-82A8-BCF9E83BBA85
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Application Specific Information:
objc[52088]: garbage collection is OFF
Assertion failed: (s->leftUntilDone <= s->sizeWhenDone), function tr_torrentStat, file /Users/transmission/hudson/workspace/trunk-mac/trunk/libtransmission/torrent.c, line 1299.
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 libsystem_kernel.dylib 0x00007fff8dd53ce2 __pthread_kill + 10
1 libsystem_c.dylib 0x00007fff956627d2 pthread_kill + 95
2 libsystem_c.dylib 0x00007fff95653a7a abort + 143
3 libsystem_c.dylib 0x00007fff956865de __assert_rtn + 146
4 org.m0k.transmission 0x000000010006803e tr_torrentStat + 1830
5 org.m0k.transmission 0x0000000100020c5b -[Torrent update] + 25
6 org.m0k.transmission 0x0000000100025676 -[Torrent(Private) initWithPath
7 org.m0k.transmission 0x0000000100020585 -[Torrent initWithHistory:lib:forcePause:] + 280
8 org.m0k.transmission 0x0000000100003ed6 -[Controller awakeFromNib] + 1677
9 com.apple.CoreFoundation 0x00007fff8e4139e1 -[NSObject performSelector:] + 49
10 com.apple.CoreFoundation 0x00007fff8e413962 -[NSSet makeObjectsPerformSelector:] + 274
11 com.apple.AppKit 0x00007fff92bbdc27 -[NSIBObjectData nibInstantiateWithOwner:topLevelObjects:] + 1245
12 com.apple.AppKit 0x00007fff92bb41b9 loadNib + 322
13 com.apple.AppKit 0x00007fff92bb36b6 +[NSBundle(NSNibLoading) _loadNibFile:nameTable:withZone:ownerBundle:] + 217
14 com.apple.AppKit 0x00007fff92bb35d1 +[NSBundle(NSNibLoading) loadNibFile:externalNameTable:withZone:] + 141
15 com.apple.AppKit 0x00007fff92bb3514 +[NSBundle(NSNibLoading) loadNibNamed:owner:] + 364
16 com.apple.AppKit 0x00007fff92e26355 NSApplicationMain + 398
17 org.m0k.transmission 0x0000000100001dd2 main + 108
18 org.m0k.transmission 0x0000000100001d44 start + 52