Windchill is soooo lacking in the ability to delete objects.
Right now as a matter of fact I have a family table of assemblies. 5 instances on a generic. They were all at version 7.4 and Production Released. Someone accidentally revised one of the instances to 8.1 back when we were in PDMLink version 10.1. I was able to delete something like this back in that version. However, we "upgraded" to 11.0 this past Oct and now it won't let me delete version 8.1. I put a ticket in to PTC about it and they said the message I see now was added in 10.2:
To successfully execute this operation all modified family table members must be selected together.
The revised instance was not being used on anything since that time. I checked all where-used files.
The tech support person now says they will have to create a patch to remove it from the database.
I checked. It is not referenced by anything. Nothing was checked in with that specific version (8.1) to the database and it's not referenced by any change object.
I just ran into this very same problem. I found a few articles on a similar issue:
I had to ask the user (luckily I knew exactly who to ask) to check their workspace for the generic assembly, and if they found it, remove it from their workspace. Even though the error I received mentioned the generic had been modified, in reality it hadn't. But, the system saw it on that user's workspace and somehow thought it had. Sure enough, once he removed it from his workspace, I was able to delete the unnecessary revision without an issue.
It was in someone's workspace. I just had them remove it but it still won't let me delete it.
To successfully execute this operation all modified family table members must be selected together. Assembly - xxxxxxxxx.asm, 7.4