If the stock usage period is incorrect, this may cause the stock usage figures to be come corrupted, this can be corrected as follows:
Log all users out of the system
Go to System
Click Application Configuration
Click System Parameters
Click Stock Control
Click the Save button to advance to the second page of settings
Set the Current Month for Stock Usage to be the number of the current calendar month (e.g. 1 for January), then click Save multiple times until you are returned to the main System Parameters screen
Click Stock
Click Product Updates
Click Item Master Mass Change
Click Special Updates
Select the Recalculate Stock Usage option and then click Save