Originally Posted by
ComputerNerd
Open the bartender options (/bt), expand the Bars submenu on the left side and click the bar you wish to page.
There should be 4 tabs, click the 3rd one "State Configuration".
Under that should be a checkbox that is titled "ActionBar Paging", check that.
Select the dropdown "Default Bar State", and select the first or default bar you want it to be.
Now make sure there are no other buttons bound to shift+1-6.
Also check the default UI option for self/focus targeted since it is possible the shift modifier applied to either might interfere, not likely set as such by default but worth checking.
(Esc, Interface, Combat - Focus Cast Key/Self Cast Key)