Code not working on locked machine

Hi

I am on IE8, winXp SP3. the below mentioned code doesn't work when the mahcine is locked. It does work though when it is unlocked.

WinWait("File Download")
WinActivate("File Download")
sleep(500)
ControlClick("File Download","","Button2") ; this clicks the default "save" button on the first dialog

WinWait("Save As") ; Wait for the "Save As" box to pop up
WinActivate("Save As")
sleep(500)

$filename=ControlGetText("Save As","Save &in:","Edit1") ;Get the file name before we erase it
ControlSetText("Save As","Save &in:","Edit1","") ; erase the file name to make room for the $dest string
sleep(1000)

ControlSetText("Save As","Save &in:","Edit1", $oDest) ; set the Edit1 text to the $dest and hit the button to swithc directories.
ControlClick("Save As","","Button2")
sleep(1000)

ControlSetText("Save As","Save &in:","Edit1", $sFileName) ; reset the name of the file to the original value.
sleep(1000)
ControlClick("Save As","","Button2")

Can some one please look and instruct?

regards