unable to download images from canon5Dmark3. Light room says unable to show preview?
Sue, LR4.1RC on Adobe labs here will import the 5DmkIII files. With that you won't need DNG. If you want DNG convert the CR2 files in Lightroom in the Library Module under LIbrary>Convert to DNG.
Are you trying to import via a direct camera connection? I think that process is pretty inconsistent (I noticed last night that I got the same from my 5DII), but although the previews aren't shown the files generally do import OK. Tried a card reader?
You may be experiencing the outworking of a known bug that is specific to 5d Mkiii. Typically, it results in the previews taking a long while to appear and actual import to take even longer. In my case the first preview may take 20 seconds or more to show. The first file to actually appear in Lightroom might take another minute, and import of all files more than 5 times longer than normal.
Note that witching to DNG might help, it did so only marginaly in my case.
QE are aware of the issue and working to find a fix.