One possibility is that the assets were using a straight-line depreciation method and at some point in their lives were put into a state of under-depreciated.  Have you run the Depreciation Adjustment Report?  If not, pull it up and check to see if any under-depreciated assets listed are the same as those that you identified.  If so, the Book Overrides tab is probably showing the None option for handling adjustments.

The easiest way to fix under depreciated assets is called the "Manual Method". Make sure you have a backup before performing these steps (File | Company Utilities | Backup Company).

After bring the asset up into the Asset List, Click the Print Detail button at the bottom. You only need to print the Main tab. Next change the Beginning Date to the date of your current period or next period. You can use any date. Enter the amount that was left over as the Net Book Value + any other depreciation calculated that year if any into the Beginning Year to Date field (Net Book Value + Current Year to Date = Beginning Year to Date). Enter the full Acquired Value as the Beginning Accum. This will manually force the asset to be fully depreciated i.e. zero Net Book Value. You will need to do a manually post to your G/L for the amount you had left over as the Net Book Value. Also rerun depreciation on the asset so it shows on the Depreciation Expense Report again.