I believe that you cannot read an integer or a string from a text file that you've created. Those must have been written by AppGameKit, and AppGameKit writes them in its own format.
To read in lines from a text file, use ReadLine(1) instead. That will read in each line as a string, and you can convert the string into an integer using Val(). Note that there is a bug with Val() where it only converts to integer, so you cannot use this technique with floats.
To use floats, you would need to switch back to ReadFloat(), but you would also need to have written the data into the file using AGK's notation.