I'm having the same issue. Both computers using latest beta (i updated because i was having the same problem with the general release. I'm trying to sync a library containing about 3500 mp3 files. The program crashes at a different point in the sync each time. I don't see a way to attach a file, so here's the tail of two logs:
example 1:
0022875: 1500: Database: CDataHolder::Load: Field: Playback Info; Files: 4190; Pointer bytes: 28; Data bytes: 4096; Elapsed ms: 10.125
0022875: 1500: Reader: CLocalReader::OpenInternal: Opening: C:\Documents and Settings\Christo\Application Data\J River\Media Center 12\Library\field (playback info).jmd
0022875: 1500: Database: CDataHolder::Load: Field: Playback Info; Files: 1024; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 3.876
0022875: 1500: Reader: CLocalReader::OpenInternal: Opening: C:\Documents and Settings\Christo\Application Data\J River\Media Center 12\Connected Library\field (audio analysis info).jmd
0022890: 1500: Database: CDataHolder::Load: Field: Audio Analysis Info; Files: 4190; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 4.072
0022890: 1500: Reader: CLocalReader::OpenInternal: Opening: C:\Documents and Settings\Christo\Application Data\J River\Media Center 12\Library\field (audio analysis info).jmd
0022890: 1500: Database: CDataHolder::Load: Field: Audio Analysis Info; Files: 1024; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 4.063
0022890: 1500: Reader: CLocalReader::OpenInternal: Opening: C:\Documents and Settings\Christo\Application Data\J River\Media Center 12\Connected Library\field (edit info).jmd
0022906: 1500: Database: CDataHolder::Load: Field: Edit Info; Files: 4190; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 3.955
0022906: 1500: Reader: CLocalReader::OpenInternal: Opening: C:\Documents and Settings\Christo\Application Data\J River\Media Center 12\Library\field (edit info).jmd
0022906: 1500: Database: CDataHolder::Load: Field: Edit Info; Files: 1024; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 3.950
0024875: 1500: General: TopLevelExceptionFilter: Unhandled exception -- program crashing
0024875: 1500: General: TopLevelExceptionFilter: Message: 0, wParam: 0, lParam: 0, Window class:
EXAMPLE 2:
0023735: 3872: Database: CDataHolder::Load: Field: Playback Info; Files: 1024; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 3.893
0023735: 3872: Reader: CLocalReader::OpenInternal: Opening: C:\Documents and Settings\Christo\Application Data\J River\Media Center 12\Connected Library\field (audio analysis info).jmd
0023750: 3872: Database: CDataHolder::Load: Field: Audio Analysis Info; Files: 4190; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 4.105
0023750: 3872: Reader: CLocalReader::OpenInternal: Opening: C:\Documents and Settings\Christo\Application Data\J River\Media Center 12\Library\field (audio analysis info).jmd
0023750: 3872: Database: CDataHolder::Load: Field: Audio Analysis Info; Files: 1024; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 4.135
0023750: 3872: Reader: CLocalReader::OpenInternal: Opening: C:\Documents and Settings\Christo\Application Data\J River\Media Center 12\Connected Library\field (edit info).jmd
0023766: 3872: Database: CDataHolder::Load: Field: Edit Info; Files: 4190; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 4.061
0023766: 3872: Reader: CLocalReader::OpenInternal: Opening: C:\Documents and Settings\Christo\Application Data\J River\Media Center 12\Library\field (edit info).jmd
0023766: 3872: Database: CDataHolder::Load: Field: Edit Info; Files: 1024; Pointer bytes: 0; Data bytes: 0; Elapsed ms: 3.851
0023782: 3872: General: TopLevelExceptionFilter: Unhandled exception -- program crashing
0023782: 3872: General: TopLevelExceptionFilter: Message: 0, wParam: 0, lParam: 0, Window class: