>How you open this file? For EXCLUSIVE or SHARED use? Can you post the code
where it happens?

Parameters xEvent
llok = .f.
Do case 
	case xevent = 1
		If !Empty(thisform.grd1.RecordSource) and Used(thisform.grd1.RecordSource)
			thisFORM.grd1.ActivateCell(1,1)
			Select (thisform.grd1.RecordSource)
			Scatter MEMVAR fields codcdc,tipcod,codart
			lLOk = .t.
		EndIf 	

		With thisform.shape1
			Try 
				If !Used('log')
					Use 'log' Again In 0 Order 'sessione'
				EndIf 
				.Tag = ''
			Catch to oErr
				If oErr.errorno = 1705
					.Tag = Alltrim(Str(Val(.Tag) + 1))
					.backColor = Rgb(255,0,0)
				EndIf 
			EndTry 
			Do case 
				Case Val(.Tag) > 2
					=scriviLog("last chance to access to File log ") 

					If !Used('log')
						Use 'log' Again In 0 Order 'sessione'
					EndIf 
					=scriviLog("File log now accessible ")
					.Tag = ''
				Case Val(.Tag) > 0
					=scriviLog("File log non accessible, try " + .tag)
					Return 	
			EndCase 
			If Empty(.tag)
				.backcolor = Rgb(207,224,220)
			EndIf 	
		EndWith 
		If Seek(zSessione,'log','sessione')	
&& that's the line which causes the error
			Replace oralast with Datetime() in 'log'
&&------------------------------------------------
		EndIf 	

		thisform.LockScreen = .t.
		If zTipoPc = '1'
			llenable=TmMain()
		else
			llEnable = 1
			If !thisform.godateprod(Date()) or ; 
				Datetime() - dateprod.lastagg  > 20*(zIntervallo/1000)
				thisform.BackColor = Rgb(255,128,128)
				llenable = -1
			Else
				thisform.ResetToDefault('BackColor')
			EndIf 		
		EndIf 

		If Used('log')
			Use in 'log'
		EndIf 	

		thisform.plsSTP.Enabled = llenable > 0
		thisform.container1.Visible = llenable = 0

		If llEnable >= 0
			thisform.loadcursor()
			If llOk
				If !Empty(thisform.grd1.RecordSource)
					Select (thisform.grd1.RecordSource)
					Locate for codcdc+tipcod+codart == m.codcdc+m.tipcod + m.codart
					If !Found()
						Locate
					EndIf 	
					With thisform.grd1 
						llrowheight = .rowHeight
						.rowheight = .height
						.refresh()
						.rowheight = llrowheight
					EndWith 
				EndIf 
			EndIf 
		EndIf 
		If llEnable = -1	
			thisform.LockScreen = .f.
			Release thisform
			Return .f.
		EndIf 	

		thisform.container1.txtgen1.value = ;
				Iif(thisform.GoDateProd(Date()),Str(dateprod.numbol,2) + ' - ' + Str(dateprod.numord,7),'')
		thisform.LockScreen = .f.
		*------------------------------------------------------------------------		
	case xevent = 2
		=TmConsuntivo()
EndCase 		

this procedure occurs every 30 seconds