Hi!

We are aware of this bug that affects the Scheduling of Avast Cleanup when it is the 31th of the month. It will be fixed in the next release (Avast 2015 R4).
In the meantime, disabling the scheduling in Avast - Settings - Tools - Cleanup - Customize - Scheduling, or setting it to a date other than 31th should bypass the bug.

Sorry for the inconvenience.