Getting the error "Manual task constraint date can not be updated" when changing Project Task's State
The affected Project needs to be recalculated.
Once the Recalculation is performed, all dates, constraints, and dependencies that need to be corrected will be fixed.
Afterward, you will be able to change the State of the Project Task throwing the error.
To do so, follow the steps below.
1. Navigate to the Project
2. Select the "Project Diagnostics" Related Link
3. Select the "Recalculate" Diagnostic
4. Click the "Run Diagnostics" button
5. Once finished, change the state