Dear,
This has been a common problem and it is related to changing the Unit of Measure schedule of an item in inventory. It has been thoroughly elaborated Mr. David Bader; a support engineer.
You need to review which item's unit of measure has been modified lately, the main point to be taken into consideration that in case the old UOM schedule and the new one have the same units this error will not occur, while it will in case new units have been added to the unit of measure schedule.
As for changing the unit of measure schedule, there are several ramification that need to be considered before changing the UOM schedule. There is certain modification that is not allowed when changing the UOM, it is simply adding new units.
Review KB article 878352 for further details.
Best Regards,
Mahmoud AlSaadi