Following the technote "Fixing broken hyperlinks with Administrative VOBs", check if you don't have a missing hyperlink between your vob and your admin vob (which, if you are using UCM, should be a PVob).
An AdminVOB is a normal VOB that will be principally used to store globally defined metadata types (branch, label, attribute, elements and hyperlinks). See here for more.
Example of resolution (here in the case of a global type being a branch):
cleartool unlock vob:\ClientVOB
cleartool describe -long vob:\ClientVOB
Hyperlinks:
AdminVOB@53@\ClientVOB -> <object not available>
cleartool describe -local -long brtype:MyBranch@\ClientVOB
GlobalDefinition@54@\ClientVOB -> <object not available>
cleartool checkvob -hlink vob:\ClientVOB
cleartool describe -local -long brtype:MyBranch@\ClientVOB
cleartool checkvob -hlink brtype:MyBranch@\ClientVOB
cleartool mkhlink AdminVOB vob:\ClientVOB vob:\AdminVOB3
cleartool mkbrtype -global -acquire MyBranch@\AdminVOB3
Doing all of this can be very lengthy in a case where numerous metadata types are broken, especially when it has to be done in all VOBs.
This could be scripted to automate the process.
Another cause: technote "Deleted user accounts and ClearCase performance":
A user account that no longer exists, but is still listed in the -nusers option for cleartool lock of a branch can cause a checkout, checkin and merge to fail like:
So if you have a lock on a branch, that can also be an issue.