When a batch containing transactions with errors is posted, those "bad" transactions are placed into a new batch marked "Errors" (maybe an Import process will do the same thing - haven't tested). The most common reasons are a closed Fiscal Period or an invalid GL account code. To diagnose the error, look at the Batch Listing report. The bad transactions will have a number in the right-hand column. That number will correspond to the list of possible problems listed at the bottom of the report.