I get this error when I have a Tab Container inside a tab Container. Example Tab container 1 has three apnels. Panel 1 has tab container 2 in it. This works fine.
Add a Tab Container to Tab Container 1 Panel 2 and you get this error
htmlfile: Can't move focus to the control because it is invisible, not enabled, or of a type that does not accept the focus.
I am using the lastest version of Ajax from 1/2013. I tried 6/2012 and 9/2012 but they don't work either.