Shevy,
Are you getting the error on the first line or the seek() I thought it was the seek throwing the error. If both lines are then your textbox is most likely not contained at the thisform level. Is it on a page of a pageframe? If so you'll have to include that in your reference:
thisform.pgfMain.pagClient.txtPgNo
>I am running this code in a cmdOK.click which is a commandbutton contained within the form.