My guess would be some kind of corruption in the INVTXN file for a record for that item.  Can you see it in Maintain Database?

i fixed it,  
 
first by making sure all users were out. then i made sure the operating system didn't have any files locked ( which i think there were some)  
did a reboot of the server,
then did a Rebuild of the bkicmstr, bkicloc, mticmstr using the pervasive rebuild utility.
 
then i ran sm-j-c at their server running 1st the master level, then seperately running the transaction level.
 
i suspect some record was locked by the server o/s which caused the initial problem.