@Zuellni: it is the same problem.

Platform: Windoes Vista x64 Ultimate
ISP: Alice (german)
Type of Internet Connection: DSL
Internet Connection Speed: 16Mbit/s
Date & Time: Any
Frequency: Always

Reproduction Steps:

1. Start Final Fantasy XIV (fullscreen mode - any resolution)
2. Once in the main menu or in the game press ALT + TAB

Result:

The Game is sent to the task bar and sound continues to play, but a DirectX error occurs: "Unable to detect DirectX device. The program has shut down. Please restart FINAL FANTASY XIV.". Once the error occured pressing the OK-Button in the error window shuts the game down completely.

The bug also occurs whenever a program or service running in the background forces FINAL FANTASY XIV to the task bar, like the Windows Vista/7 Account Control or the Windows Update service.

Expected Result:

The game should not show an error message when it is forced to the task bar and resume normal operations once it regains fullscreen capability.