You need to keep checking from the flash file
you can loop in flash to check to see if a file on the server has changed. eg: say your asp page has finished doing whatever:
if you're not familiar with the fso object then use this sub to save text files to the server:
private sub writeTextFile(strContent, strFilePath)
set fso = createObject("Scripting.FileSystemObject")
set f = fso.openTextFile(server.mapPath(strFilePath), 2, true)
set f = nothing
set fso = nothing
So do whatever you want to do with your asp and then save a file to the server
for i = 0 to 100
response.write "this is the " & i & "th time I've done this..." & "<br />"
if i = 100 then
writeTextFile "done=true", "myfilePath.txt"
then on an onenterframe loop in flash keep checking whether the myFilePath.txt file has a variable called done that == true using loadVariables (google it if you don't know how: it's easy...)
That way your asp can report back.