nigeld27

For any future readers, the error was caused by our Hubspot Tracker Code being in the "Page View Javascript" (in Page Outputs) that caused the problem. Thank you @opentype for helping me figure it out.

Hi Daniel,
 
I thought Member ID = their email address. I've just gone into the Invision members area and cannot see Member ID fields. 
 
If you are not in front of your computer, this is not super urgent. Perhaps neither of us should be working on Saturday!
 
Thanks,
Nigel 
That worked. I did not know that there was a difference between email address and ID. 
 
Thanks @Daniel F, @Jim M and @Marc Stridgen.

Thank you for the respnose @Randy Calvert.
 
I worked it out. I created the page in a new folder which I named "Admin", meaning the subdirectory was domain.com/admin/page-name. The /admin is the AdminCP!
 
If anyone from Invision sees this, maybe you should ban people from creating an 'Admin' folder for pages, in case an idiot like me creates it.

Thank you @Paul E. that is helpful. I switched to GD and increased the image size limits and now the gifs are working. 

Hi Everyone. I have updated to 4.5.1 Beta 2 and the problem appears to be fixed.