This usually happens when opening the Toolbox (CTRL-ALT-X), or moving the mouse over the Toolbox icon (which appears on the left).
According to this Connect issue report, there’s a workaround to be done, which may fix the issue:
He said he simply removed the registry key under:
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\
VisualStudio\10.0\Packages\{D766DAA8-F81E-4621-9184-F21C7F389796}
and the problem went away. Read more on that link.
- Be sure to take a backup of whatever registry changes you make!