I use Lightroom to convert my CR2 Files to dng. The export doesn't embed the original files, the preview is medium size, the containing data is not changed (developed) until here. So far, the exported dng can be shown with Irfan View without problems.
Then I adjust the development settings in Lightroom and let it update the dng preview. The created dng cannot be loaded with Irfan View resulting in "Decoding error! Not a valid RAW file" message. Updating only metatags and keywords seems not to make the file unreadable.

Is there anything I can do to to make it working?
(Of course, I could left the update of the development data, but then the dng preview picture usually looks ugly.)