I'm having the "invalid buffdirty call", when i tried to delete some records of a free table

example:

sele table1
dele for table1.field1<=date()-30

sele table2
dele for table2.field1<=date()-30

sele table3
dele for table3.field1<=date()-30

sometimes table1 make the call, sometimes two of the tables, sometimes every table, i solved this copying the records to a new table, zapping the table and append the records from the new table.... but, i don't want to do that

what's going on??

TIA