One of our rucksacks has started generating an error when we try to open it. Any ideas as to what might be causing this?

Exception occurred in application Recorder 6 at 16/09/2008 16:57:05.
Version : 6.13.2.176

Exception path:
EVariantTypeCastError : Could not convert variant of type (Null) into type (String)
ERUKError : Unable to complete file operation.  Please ensure that the rucksack has not been deleted

Last event\actions:
  actRuckSack invoked
  TfrmRuckSack created
  TfrmRuckSack activated

Operating System : Windows XP  5.01.2600  Service Pack 3
Physical Memory available : 2,097,151 KB

DLLs loaded:
  advapi32.dll (5.1.2600.5512)
  comctl32.dll (5.82.2900.5512)
  comdlg32.dll (6.0.2900.5512)
  gdi32.dll (5.1.2600.5512)
  gdiplus.dll (5.1.3102.5581)
  HHCtrl.ocx (5.2.3790.4110)
  kernel32.dll (5.1.2600.5512)
  mpr.dll (5.1.2600.5512)
  MS5.Dll (5.0.0.12)
  MS5User.Dll (5.0.0.4)
  odbc32.dll (3.525.1132.0)
  ole32.dll (5.1.2600.5512)
  oleaut32.dll (5.1.2600.5512)
  shell32.dll (6.0.2900.5512)
  user32.dll (5.1.2600.5512)
  version.dll (5.1.2600.5512)
  winmm.dll (5.1.2600.5512)
  winspool.drv (5.1.2600.5512)

Information has been saved to the file T:\Recorder 6 Server\User Files\LastError.txt