Thanks, I think I understand what part of the problem is now.
From your Gantt video it doesn't look like you have set up any dependencies between tasks and yet when you changed the % from 99->100 the program prompted you about dependencies.
Some time ago (from memory) there was a bug where all tasks were incorrectly assigned an empty Dependency attribute which might account for this issue. If you make the Dependency column visible (View > Task Attribute Visibility > Dependency) you might see the orange icons like in the following image:
![](https://lh3.googleusercontent.com/-JgV-KMfo1HY/WYL_Dsl6EhI/AAAAAAAAAgI/xM_02hXzwuELA0etcp6hMBvyQDm7VHxVACLcBGAs/s320/dependencies.PNG)
If you do see these icons and you didn't create any dependencies yourself then we must clear this field first:
1. Switch to the 'List View'
2. 'Edit > Select All'
3. Mouse-click in the Dependency edit field
![](https://lh3.googleusercontent.com/-boBRLPaoK8Y/WYL_9EI-x9I/AAAAAAAAAgQ/OritXfUER84T_2Ng8dArVrY30Qdc3aUgQCLcBGAs/s320/fields.PNG)
4. 'Edit > Other Task Attributes > Clear Focused Task Attribute'
Let me know how you go...