When running an SSIS project, I was getting a very strange error: All data flow components of a child package succeeded with green check marks, but the entire package is marked with a red cross, indicating that it failed. In the "Progress" log, the error says: [... ] Error: Category does not exist.
It turns out that the error was caused by a debug break point in a script component. Debug break point in a script component usually works, but when a data viewer is turned on, or an earlier debug break point was hit in a different script component, a subsequent debug break point in a script component would usually fail, probably due to lack of available RAM or something.
This type of failure would be harmless if the package is the last one in the control flow. But if it is in the middle of the control flow, the entire task would fail.
The fix is easy, of course. All you would need to do is to open the script component source code, and remove the break point.