Hello. I have been using SS2.3+ sucessfully on the hosting platform that i use in South Africa. I recently started working with SS2.4+ but i keep on getting "File is not a valid upload" errors when attempting to upload files/images after doing fresh installs on the host server. On my local machine that runs WAMP, everything is perfect.
I have checked the forums and most of the posts relating to this issue is really old and i would assume would have been dealt with already in the new version 2.4.2. The only thing that i can think of is that there is a hosting parameter that my provider does not meet.
I have dowloaded SS2.4.2 and the same problem persists. It is only the file uploads that does not work, the rest of the CMS is perfect.
Your problems are probably caused by a PHP open_basedir restriction set by your service provider. This patch should help you get up and running: http://open.silverstripe.org/attachment/ticket/5547/2.4.1-FileUpload-2.diff
You may also want to check out [url=http://open.silverstripe.org/ticket/5547]the ticket for the issue[/url] and [url=http://ssorg.bigbird.silverstripe.com/general-questions/show/281744]this forum thread[/url].