I also get this error, but for the \rdsdbdata\db directory. We're running MySQL on Amazon RDS. I'm guessing Mango does not have permissions to view the file system, or is treating \rdsdbdata\db as a local directory when trying to view the usage?
As Fox asked, any way to disable this check to save some errors in the log file?
I could see this being a new feature/change to the way it works. Instead of only having a single delay task we could have many. For example if your meta point is context updating every 1s and your execution delay is 1hr after 1hr of running you will have 3600 tasks sitting around with 1 executing every second after that. Execution delays were not really designed for that though as if you were to stop mango or that data source you would lose 3600 point values in the tasks that had not yet run.