There are two possible explanations: 1) your settings for the upload on SoundCloud have "app streaming" disabled; 2) a major label or distributor has blocked SubmitHub from streaming your song. If it's the latter, your options are to a) use a different source (eg, YouTube), b) email SoundCloud to get them to "whitelist" the track, or c) upload an MP3 on SubmitHub, but put the SoundCloud link as one of your "alternative sources" -- it will be shown to the outlet if they approve.
Here's some more context on that second possibility: SoundCloud's monetization platform "SoundCloud Go!"
Sometimes, in an effort to monetize this content, labels (particularly Universal Music Group) have blocked 3rd party websites such as SubmitHub from using SoundCloud's API. More often than not, and for the sake of making their lives easy, they opt to block the entire account, and not just specific songs. So, even though your new song may have no affiliation with a major label, if an older track on your account did, it may mean *everything* is blocked.
In order to unblock your song, you'll need to ask the right's holder to email SoundCloud (help@soundcloud.com) and ask them to "whitelist" SubmitHub for your account. Otherwise, feel free to upload using YouTube. (If you're unsure who your rights holder is, you can ask at that email address).