unable to use variable for application.title in dpr?

Title says it all, but can someone explain why I can't seem to associate a string variable at runtime in the dpr to the application.title?
Everytime I put the line of code in, it disables the RUN application button, and then if I save and leave it in and try and reopen the application, it is now corrupt and I have to restart from a prvious version of the code.

I'm guessing this is just something I didn't know you couldn't do but I'm just checking.

var
  sTemp: String;
begin
  .
  .
  .
  Application.Title := 'This string'+ sTemp;