apparently we haven't tested this enough. Somehow the RapidMinerUpdate.exe got lost during the update from 5.2.8 to 5.3, which causes the error you have mentioned for the next update. We are sorry for any inconvenience this caused. Currently, we are working on this issue.
In the meantime you can use the following quick fix. Download the missing exe file
and copy it into RapidMiner's scripts directory. Start RapidMiner and if you are not prompted for the Administrator password, you have to restart Windows.