Can't install RAIDiator-4.1.9

I have the same problem on my ReadyNAS DUO. When I let the ReadyNAS download and install, the log file mentions there was an error while downloading the update image. When I manually download the update image to my mac (OS X Lion, 10.7.4) and choose the local update function, the check of the file shows no problems, however, when I choose to update the system, I get an error message as well referring to a wrong checksum. The error message is in Dutch: "Ongeldige checksum gedetecteerd in het updatebestand. Update afgebroken". This translates as "Invalid checksum detected in update file. Update canceled." I tried download + update with both Safari and Firefox.

I have a standard DUO on 4.1.8 with two 2GB drives installed which mirror each other.