TTable: Blob has been modified

We got the following error, probably in TTable.Open:
'Blob has been modified'. Our Paradox 5.0 table includes one TMemo
field. The error occurs still after reboting Windows.

What is this error message about?

Tuomas Salste  
****  Visual Basic Tools and Blonde Jokes available through my WWW page ****
----  Today's stupid blonde joke (I won't replace these!):
236. Two blondes were driving along a road by a wheat field when they saw  
     a blonde in the middle of the field rowing a row boat.  The driver  
     blonde turned to her friend and said "You know - it's blondes like  
     that that give us a bad name!"  To this the other blonde replied "I  
     know it, and if I knew how to swim I'd go out there and drown her."