I had exactly the same problem with the IDB backup schedule. I could not see any fault in the configuration files (datalist in: config/server/datalists and corresponding schedule in config/server/datalists/schedules) and had to delete/recreate it.
I just patched tonight with the latest patches. The "invalid argument" bug has not been fixed!
On top of that I'm now getting a new error: an occasional "IPC can not connect" pop up message when working with the Filesystem backup. This new error message pops up several times in a row and takes several clicks to get rid of it.
DP labs are aware of this problem and have already created a fix for that. The fix contain new GUI binaries and is internally referenced at HP with the number QXCM1000406236. Any other later GUI fix will work as well.
You need to log an officilal support case to get the fix.