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This also applies to EPiServer's thumbnails, when accessing a thumbnail EPiServer throws an error:
[NullReferenceException: Object reference not set to an instance of an object.]
at EPiServer.Core.ThumbnailManager.CreateBlob(Uri thumbnailUri, Blob blobSource, ImageOperation imgOperation, String mimeType)
Just had the same issue and indeed iisreset fixed it (for now).
I'm curious however to what causes this.
I have an ImageData content that has 3 different sizes, specified using the image descriptor attribute, ref:
http://world.episerver.com/Documentation/Items/Developers-Guide/EPiServer-CMS/75/Content/Assets-and-media/Media-types-and-templates/#ImageDescriptor
The resized images are not created correctly, and this error message is located in my log file:
ERROR EPiServer.ImageLibrary.ImageServiceClient: Exception calling ImageService RenderImage method
System.Runtime.InteropServices.COMException (0x800703FA): Illegal operation attempted on a registry key that has been marked for deletion.
This error only occurs on our test server, I works as expected locally.
Any ideas?