I know your problem (i hope)

You probably do something like

createobject('myform')

or

local loForm
loForm=createobject('myform')

What now happens is that a local object reference is created. When the routine stops this var is released
Better create a public var and store the reference to the form to this var.
When you release the form, don't forget to release the public var.

Public oMyForm
oMyForm = CreateObject('MyForm')
oMyForm.Show()