Hi Guy,
Try copying the data files to a local hard drive, and perform a single entry check on your OH data. If the DataCare does not exit abruptly to the desktop, then the issue has to do with your network environment.
If you have sample data, try the same integrity checks. If there is no abrupt end, then there is in fact a problem with this file that is not being reported.
Also, try doing a Single Start List data check with the Flat and Keyed files turned off for Invoice History. This will basically be the same as the WSM integrity check. In doing the WSM check, do you run across the same 'crash'?