If all of the package version files were successfully removed then the same package version can be added immediately without a system restart, however if any of the files could not be removed then adding the same package version that was just deleted returns error 0x8007012F. This is by design.
To work around this issue, reboot the computer before adding the same package version again. The system restart will complete the removal of the package version after which the same package version can be successfully added again.
This scenario is most likely to occur in a test environment as in production there's no reason to remove a package version and then add the same package version again. However, if this were to occur in production and if a system restart cannot be performed, there is an alternative workaround that does not require a system restart. As an alternative, you can create a new version of the same package. To do this, open the package in the Sequencer and then save it. The new package version will not be affected by the partially deleted state of the prior version and so it can be added without restarting the system.
NOTE If this problem occurs in a full infrastructure scenario then at the next "Refresh" this error will be logged in the App-V Client Admin event log.