There's a trick to mention the URL of the file when the Data.txt file is not in the same folder as the main .mxml file. For example, if your file is in a folder called News, then the URLRequest should contain the location of the file like this:
"./News/Data.txt". Ofcourse, the News folder should be in the same domain. If you need to access a file in another domain, you will have to make a cross-domain file. This I will be discussing later.
The project structure should be like this for the below code to work:
This example shows a simple Data.txt file being read.