CameraBookmark Window error

[Anonymous]

When I try to set camera bookmarks, it says the error message like object name 'CameraBookmarkWindow' is not unique. Please any one can help me to sort it out??

Camera BookmarkError Message

[daisuke.tabayashi]

The CameraBookmark Window is already open, but the window may be off screen.
In that case(windows)
1. Click the window you want to move to activate it.
2. Hold down the Alt key and press the Spacebar.
3. Press the M key.
4. Use the arrow keys to move the window.