Hi Diana,
I have many scripts in photoshop CS and the only little detail that I see is that when you say
tell application "Photoshop CS"
open alias myfile
end tell 
script editor look for this app, and then stop to ask for it, but if you say
tell application "Adobe Photoshop CS"
open alias myfile
end tell
it should works ok

I have many as is example; set MyFile to alias "MyDisk:Users:g5:Pictures:mypicture.jpg"
tell application "Adobe Photoshop CS"
 open MyFile
end tell