Sonny,
When you change the content of the RowSource of the cbo you must call the cbo.Requery(). If that doesn't fix the problem, you need to provide more detail about the property settings of the cbos that are showing up empty.
>have an application client/server, with which I charge at the beginning of my program the contents of several table of reference from ODBC SQL that I affect in combo box. At certain time in the execution of the program, some combo box is empty.