If the code I wrote was long, I would have understood your warning. I wrote 4 lines of code. You understood what the code is and you give such an answer. You could have helped until I wrote this if you knew.
It is not a warning. It is a request. It should take you two minutes to fix.
There are many new posts each day and it is more difficult for me as well as all other members, to read code that is not posted properly.
About your question:
1. Code with File.DirRootExternal = broken code.
2. If this is a new project then switch to B4XPages and forget from all such issues.
3. I cannot say anything else as the actual problem is not in the code you posted.
4. As you chose not to edit your post and fix the missing code tag, I will not further help you.