Hi,
this kind of behavior might indicate problems with texture paths - either lost or containing non-English characters, but please post the error message (Window > Toggle System Console) so that we know more details.
Cheers
Szymon
i7 5960X | 64GB RAM | Win10 Pro | ASUS X99 Pro mobo | Chieftec 1250W psu
MSI GTX 780 Ti OC 3GB | 2 x GIGABYTE GTX 780 OC 3GB on USB risers | MSI GTX 750 Ti for display
Blender + Octane | C4D + Corona
Flickr profile: http://www.flickr.com/photos/kubicki3d
System console shows no error. Actually it always stays same, If I look at the correct place.
While working I followed this path of problem, this error always happens when I toggle glossy material. Usually when I upload textures ( I checked names, no special character is included in names), but sometimes it happends when I change some values like specular or roughness even without texture. Some times it happens when I mix diffuse and glossy materials.
Usually after undoing it doesnt get fixed. File stays broken, even after reloading the file the problem endures. I tried v2.72 and 2.75, happens in both.
From your description I can only tell that I haven't ever had such a problem, unfortunately. Let's just see what System (not Python) Console says - go to Window > Toggle System Console when the problem occurs.
i7 5960X | 64GB RAM | Win10 Pro | ASUS X99 Pro mobo | Chieftec 1250W psu
MSI GTX 780 Ti OC 3GB | 2 x GIGABYTE GTX 780 OC 3GB on USB risers | MSI GTX 750 Ti for display
Blender + Octane | C4D + Corona
Flickr profile: http://www.flickr.com/photos/kubicki3d
Yes it says Error in loading image to server. It does same thing for different textures, with different sizes etc. I checked names, they are all regular characters.
I made a quick test and put a correctly named texture into a folder with some Polish characters, and System Console gave me the same message - I suggest you check all your folder names as well, it's probably best to avoid non-English characters in everything Octane-related...
i7 5960X | 64GB RAM | Win10 Pro | ASUS X99 Pro mobo | Chieftec 1250W psu
MSI GTX 780 Ti OC 3GB | 2 x GIGABYTE GTX 780 OC 3GB on USB risers | MSI GTX 750 Ti for display
Blender + Octane | C4D + Corona
Flickr profile: http://www.flickr.com/photos/kubicki3d
Some of my texture names had space instead of underscore, that might have caused problem as well.
Also thanks to your suggestion to check console, I found out about the main cause of problem. I was working in office from the server. I packed the model and copied it to local HD, this Error didn`t appear again. So I think server connection somehow interferes with Octane server, it is best to work on local storages.