If you were trying to add a driver to a boot wim and it failed resulting in that error code the following may help. 1. Clear all your temp directorys. 2. Browse to "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WIMMount\Mounted Images" and delete any keys below this. WDS should now allow you to add drivers to the boot.wim.
Stole this from the following link: (might be other suggestions there as well) http://social.technet.microsoft.com/Forums/en-US/w7itproinstall/thread/a202816a-59f6-48bb-a71a-fe2ca3add4c9