I honestly can't help with Antivirus Engines flagging the app as malware. I could possibly rewrite the download routine but that would be overkill for what the app at its current state tries to achieve.
I have open sourced the code for this very reason. I could only advise you to add the program to your exceptions list and then run it. In reality, there's nothing wrong with the app itself, it's just the anti malware engines that detect it as a false positive.
Would encrypting the EXE into a ZIP file be enough to download the file, and bypass the AV engines? You'd always have the password in the OP....