fruhling wrote: Yes. Appears to be a mod_security issue beyond my control on shared hosting.

Any idea of how to circumvent this - submitting a youtube link should not trigger this? All other forms are working fine..?

You need to contact your host and have them reconfigure the mod_security for your usecase.
It wouyld help to try to uploade again, get the error and mark down the exact time so they can check their logs.