Tri state check box in table not saving third state (on turtorial,express version)

I am a bit confused,when i run the code below it changes the checkbox to the third state buth it is not saving the third state to database.Do i need to switch the key type checkbox to aray?is there any example that explains handeling the tristate?

(key type checkbox )
status is int
status=TableSelect(TABLE_Time,1,tsRow)
COL_status[status]=-1
HModify(dbclient,status)

i tried the table with direct acces aswell as the table load in memory.no result