A mod to File Upload version 1.8.4 to make it work with vanilla 2.1.5
make sure you already have version 1.8.4 downloaded from gitthub and copy the FileUpload plugin into your plugins folder.
Do not enable the plugin yet.
you can download the addons from github here. File Upload 1.8.4 is in the Master (at least now it is)
make sure you already have version 1.8.4 of FileUpload downloaded from gitthub and copy the FileUpload plugin into your plugins folder.
download the attached zip file, unzip and copy over the existing class.fileupload.plugin.php
it worked for me as far as allowing plugin to be enabled and for uploading and downloading and deleting attachments.
also you can add info here:
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.