I got the same error in Safari. The Web Inspector reported the cause as the following:
[Error] Failed to load resource: the server responded with a status of 403 (Forbidden) (GetEntity, line 0)
[Error] Blocked a frame with origin “https://3dwarehouse.sketchup.com” from accessing a frame with origin “http://www.tcwaterstop.dk”. The frame requesting access has a protocol of “https”, the frame being accessed has a protocol of “http”. Protocols must match.
Hg (compiled.js, line 1013)
(anonymous function) ([native code], line 0)
(anonymous function) (compiled.js, line 259)
handleEvent (compiled.js, line 121)
wh (compiled.js, line 129)
vh (compiled.js, line 129)
xh (compiled.js, line 131)
dispatchEvent (compiled.js, line 134)
fz (compiled.js, line 242)
(anonymous function) ([native code], line 0)
handleEvent (compiled.js, line 121)
wh (compiled.js, line 129)
vh (compiled.js, line 129)
xh (compiled.js, line 131)
dispatchEvent (compiled.js, line 134)
dk (compiled.js, line 230)
fk (compiled.js, line 232)
Bq (compiled.js, line 231)
Tu (compiled.js, line 231)
(anonymous function) ([native code], line 0)