WebPlus X6: Is there a restriction with Movies?

hi, I am attempting to publish my first website. It works ok in Preview. However, when I try and publish, it fails when it tries to upload the only movie on the site.

It is an MP4 file 7.83Mb in size. It always gets to 10%, then re-tries. After 3 re-tries I have to cancel the operation.

I have a Gold subscription to Serif hosting. I could remove the movie if need be, but wondered if there was some kind of restriction I'm unaware of as the movie plays ok in preview.

thanks