Too Many Open Files

Situation

A backup plan on macOS fails with the following error: Error on processing some files.

This error is also displayed in the History tab with the following message: Too many open files.

Cause

macOS limits the maximum number of files a given process can open simultaneously. The error implies that the product is trying to exceed this limitation.

Solution

Reduce the max thread count to 5. To do this:

1. Click the Settings icon, then switch to the Advanced tab.
2. In the Max thread count field, enter 5.

3. Click Close.