Adding to Mariannes excellent post ...
... this is what Marianne means by 'delete'
You can remove the image from SLP control:
nbstlutil cancel <backupid>
WARNING: If the image is 'capacity managed' and, the time it should have expired is past
If the backup is for expiration of (eg) 1 week, before it is duplicated, SLP makes it infinity, and will set it to it 1 week expire when it is duplicated. As this hasn't happened it is still infinity. If this image was taken say 2 weeks ago, if it was to duplicate, or you manually remove it from SLP control with the above command, it will expire 'instantly'. There is no way round this that I know of.
Anyhow ...
Once you habe removed the image from SLP, you can manually use bpduplicate to copy it.
Your vendor is sort of correct, SLP images cannot be forced to run using standard NBU commands, but they can be copied as above.
The bigger issue, is why is the image in this state, it should not happen.
The db (where the image state is stored) can get messed up, for example if the server crashes, so it may be that things need sorting out. Not sure what version you are on, but you may wish to check if you have any available SLP patch.
WIth SLP issues, don't leave them (I'm not saying you have ...) get onto Symantec support quickly. If left, the issues can build up and up and be virtually impossible to sort within the expectations of the customer, as many people run their system at 100%, that is backups and dups 24/7 . Therefore if the system gets behind, there is no available time to catch up, and suddenly the most simple small issue is a major problem.
Martin