I had a strange issue with a tour that was working perfectly in normal browsers but was throwing a string of errors if I tried to access it via any iOS device.
The first error was WARNING: tween type " not found - using 'easeOutQuad' instead! followed by ERROR: hotspot[logo0] loading error: virtualtourdata/graphics/logo0.png and then the tween error just kept repeating itself a lot.
Directly accessing the logo0.png in the iOS safari browser worked so it's not that the file is missing or a permissions error. Then I loaded the png on my desktop and noticed that it's a huge png in terms of pixels (small kb) but it was 2638x2350 pixels so I reduced it to something more sensible and uploaded it to replace the large one and now the tour works without throwing any errors on my iOS devices.
Obviously I shouldn't have had the nadir png so big in the first place but as it is resized I didn't notice on a desktop browser. The HTML krpano doesn't seem to like nadir logos being larger than the tile sizes generated for iOS devices, and quit rightly so, but I would have thought it would catch the error in a nicer manner and perhaps just hide the nadir logo rather than throw errors like this?