If you want to insert a NULL value to this filed you don't have to include the field on the insert list. However, in the values list you sent there is an error. You sent:

&& Save event
>> INSERT INTO rv_EMPFILE(field1, field2, field3);
VALUES(alltrim(thisform.txtbox1),;
alltrim(thisform.txtbox2),;
alltrim(thisform.txtbox3))

You must include .value in the the text objects in the values list. For example: instead of "thisform.txtbox1", write "thisform.txtbox1.value".

I hope I've helped...

Silvio