ITCA CA Client Automation / ITCM IT Client Manager -- any version.
This can happen if a new package is being made and the process is interrupted during the addition of files to the package source before the package is sealed. When files are being added to the package volume, the manager 'locks' the package so no one can attempt to use or seal it as a modification is in process. This activity is normal and normally the lock is removed once the modification is completed. When interrupted however, the connection to the DM can be severed and the package can remain locked, preventing a retry of the operation or even a deletion of the package at all.
The lock on a package in this case is held in RAM Memory on the Domain Manager and not in any file or database entry. The only solution is to reboot the Domain Manager to clear the lock applied to the package that resides in memory.