Graham, have you tried looking in the logs for any clues?
Here's the log for the past few minutes when I tried to start eXposure:
>> Log file started at 2009, Apr, 08, 15:04:54
Added debug context 'GUI '(1196771616) at index 1
unset channel 255
Added debug context 'ACOR'(1094930258) at index 2
Added debug context 'IMGL'(1229801292) at index 3
Added debug context 'DNGL'(1145980748) at index 4
Added debug context 'DNG '(1145980704) at index 5
Added debug context 'eyeR'(1702454610) at index 6
Added debug context 'JPEG'(1246774599) at index 7
Added debug context 'TIFF'(1414088262) at index 8
Added debug context 'HCOR'(1212370770) at index 9
Added debug context 'CCOR'(1128484690) at index 10
Added debug context 'eMoB'(1699573570) at index 11
eMotion_helper::eMotion_helper()eMotion Back - instance created: 0x1d5a934
Added debug context 'eSpB'(1699967042) at index 12
initializing FireCamJ now
Added debug context 'eVoB'(1700163394) at index 13
Added debug context 'C645'(1127625781) at index 14
Added debug context 'H H1'(1210075185) at index 15
Added debug context 'H V '(1210078752) at index 16
Added debug context 'M6FD'(1295402564) at index 17
Added debug context 'M6TL'(1295406156) at index 18
Added debug context 'M RB'(1293963842) at index 19
Added debug context 'M RZ'(1293963866) at index 20
Added debug context 'R608'(1379283000) at index 21
Added debug context 'R60X'(1379283032) at index 22
Added debug context 'RLCl'(1380729708) at index 23
Added debug context 'SLCl'(1397506924) at index 24
Added debug context 'SCMV'(1396919638) at index 25
Added debug context 'SCZL'(1396922956) at index 26
Added debug context 'SCPL'(1396920396) at index 27
Added debug context 'SHLV'(1397247062) at index 28
Added debug context 'SI_M'(1397317453) at index 29
Added debug context 'XCnt'(1480814196) at index 30
HCMemoryMgr::HCMemoryMgr() stores temporary items to: /Users/grahammitchell/Library/Application Support/Sinar eXposure/Temporary data/HCData
HCMemoryMgr::HCMemoryMgr() free space in temporary folder is :11894 MB
"15:04:55.918" int main(int, char**) Sinar eXposure "ExpS" "6.1.1" ( "184" )
"15:04:55.919" int main(int, char**) Looking for GUI plugins in "/Applications/Sinar eXposure.app/Contents/PlugIns"
"15:04:55.920" int main(int, char**) OS: MV_LEOPARD (10.5)
"15:04:55.922" int main(int, char**) Wordsize: 32 bit
"15:04:55.923" int main(int, char**) ByteOrder: BigEndian
"15:04:55.924" int main(int, char**) Total availible virtual memory: 3070 MB
"15:04:55.925" int main(int, char**) Total physical memory: 4096 MB
"15:04:55.926" int main(int, char**) Number of physical cores: 2
"15:04:55.927" int main(int, char**) Number of logical cores: 2
"15:04:55.933" int main(int, char**) Locale "GUI_en_GB" loaded from "/Applications/Sinar eXposure.app/settings/"
"15:04:55.959" GUIMemoryMgr::GUIMemoryMgr() memory limited to "2.30 GB"
"15:04:55.960" GUIMemoryMgr::GUIMemoryMgr() unpurgable memory used so far "331.31 MB"
"15:04:55.961" GUIMemoryMgr::GUIMemoryMgr() availible application max "1.98 GB"
"15:04:55.961" GUIMemoryMgr::GUIMemoryMgr() availible internal application max "1.38 GB"
"15:04:56.044" GUIHelpManager::GUIHelpManager(QObject*) Tooltips "ToolTip_en_GB" loaded from "/Applications/Sinar eXposure.app/settings/"
"15:04:56.146" void GUIStatusBar::loadSettings() Camera sound file does not exist.
Does that help at all? Is the last line a clue?