I had an interesting problem today. One of the developers told me a nightly job had stopped with an error. I check the usual things like has anything changed and was told no. The error was sent to me and was the following:
SQL*Loader-926: OCI error while executing delete/truncate (due to REPLACE/TRUNCATE keyword) for table REPORT_TEMP
ORA-01502: index 'PK_REPORT_TEMP' or partition of such index is in unusable state