>I have a grid with 8 columns. Columns 2 and 4 have a combobox.
>on click column 4 works.
>when click column 2 and then click column 4: !!Doesn't Work. Message: Cannot Access the selected table (Error: 1152)
>The tables are in the dataenvironment. (VFP5)

What is combo.rowsource? If it's view/cursor and you override rowsource on fly, then you should firstly reset it:
Combo.Rowsource=""
then recollect rowsource (SELECT_SQL?) and set it back:
Combo.Rowsource="mycursor"