Had similar issue with Archos 97 Carbon tonight but issue is now resolved.  This is what happened and what I did.

Used Rockchip Batch Tool V1.5 with kasty-arc97carbon-40-042-2G and clicked on Upgrade not Restore, which ended up with prepare "idb fail" message.  Unplugged device and rebooted it and it worked the same as before.

Tried again using Restore this time, but device failed at about 80% of "Lowerformat" process and would not turn on, just a black screen although Rockchip Boot Tool V1.5 did display it as a green box.  Tried a few more times but kept getting the same error message so figured it was time to buy my daughter another one.

Decided to give it a go with Rockchip Batch Tool V1.6 although it did not currently say it worked with the Archos 97.  Tried the Restore option again and this time it made it to 98% but failed again.  Thought I was getting somewhere now so decided to connect the device using my HTC USB lead instead of the Archos supplied one and again used Rockchip Batch Tool V1.6 and the Restore option.  Thankfully it made it to 100% and eventually I got the green Restore Done Success message...took 233565ms to complete.

Installed Root Checker Basic and it confirmed I had Root access and checking Storage it showed 1.97GB instead of 504MB.

Unfortunately though Chrome and Angry Birds continue to shut down prematurely which I had hoped this would resolve but at least I got the device back.