I get a "not a valid script file" error when trying to import.
Edit: changed the first line to <?xml version="1.0"?>, repackaged and it worked.
Edit 2: After importing, I get "Error: Invalid root in registry key". This can be solved by checking if the user is signed in in the OnEvent_Initialize function, and then if they are call the OnEvent_Signin function passing Messenger.MyEmail. This way the user does not have to re-sign in for the script to work.
Also, one way to solve your removing the text from the text box problem would be to use ChatWnd.EditText_SetCurSel - look in the scripting doc for more info