Back in March I wrote the following article: Dynamics CRM Developer Tip O’ the Day: Working with Tabs.
Xrm.Page.ui.tabs.get(0).sections.get(6).setVisible(false); // Hide section
Don’t ever do that! Bad developer! Bad!
So again, never, ever use the numerical value to reference a Tab or a Section, unless you have no choice.
We don’t want to use numbers because if you move or add Tabs or Sections, your code will no longer work.
Do this instead:
Xrm.Page.ui.tabs.get("General").sections.get("Details").setVisible(false); // Hide section
As long as your Tabs and Sections are named properly, you should not have an issue.