OK, so I have (had) a file which is no longer found on disk, but there is no option in Worksession manager to remove a file which has been removed from disk. Such an option should be added.
So, of course I try a workaround by creating a fake file with this name and filepath, but then Rhino cunningly replies like so:
Hm. Now what? How do I clean out that missing file reference?
// Rolf
Hi Rolf - just highlight it in the list and poke ‘Detach’… does that do it?
-Pascal
No, all buttons are dead, except for Attach… 
But what if you highlight that item in the list?
-Pascal
Yes, I tried that, but all buttons are dead except for Attach (sorry that my first screenshot didn’t show that I meant that the buttons were dead while selecting the missing file ref):
Like so. No option to detach:
// Rolf
Ok, I see - I tried to reproduce the situation and I was able to select and detach the file… let me have another go…
I get this on opening a rws file for which one attached file has been deleted:
---------------------------
Rhino 6 Open Reference File Error
---------------------------
Unable to read the reference file named
C:\Users\pascal\Desktop\Junk\SyncViews.3dm.
When Rhino is finished reading the work session file, you may
use the "Worksession" command to edit the list of reference files.
---------------------------
OK
---------------------------
then I see this, in Worksession:
and
So I am doing something different but I do not see what yet.
-Pascal
Try rename “SyncViews.3dm” and open Worksession. Then close WS and remove the file and try open WS again. Are you then out of option to detach?
BLOCK (Worksession)
I have another problem with Worksessions. if I open a file (part of WS) and start inserting a block, but then aborts the insertion before confirming the insertion, then I still see the Block’s layers show up in the file (not expected) but no block in the Block manager (as expected). And if I try to delete those layers it refuses due to a Block definition on the layers (which are not there, at least not visible in the block manager.
Solution: Close Worksession altogether and open the individual file, then it allows you to remove the aborted block insertion layers.
Perhaps this post should be split, but it seems to be a problem with Worksessions messing up files/references in runtime.
// Rolf
Hi Rolf - hmmm- so far it all works. …
-Pascal
Can it be related to me opening old R5 files and then saving them to R6 and… somehow Rhino gets messed up?
(But I did introduce Worksession only today, not in 2016 when the individual files were first created).
Hi Rolf - can you repeat the setup from scratch? If so, please give me the blow-by-blow, there is something I am missing…
-Pascal
Yup, I finally was able to reproduce:
So #3 makes all the difference (If any other Model file is active when deleting Model A.3dm, then the error does not occur, so I also struggled with reproducing this… 
)
// Rolf
Hi Rolf - thanks, I’ll test this.
-Pascal
Hi Pascal, has this been looked at lately? I also have the same issue.
Thanks
First few minutes working on my Worksession to experiment with it before integrating it into the workflows and this big issue pops up: Work Session Attach Failed.
The file is already attached to work session.
I will not use “set active model” until this bug is fixed because it destroy my first worksession.
Always buy design bug
The button “Detach” is hidden or inactive. If I try to attach that file a warning message pops up.
Expected: The button “Detach” is active and it is possible to take out the reference and reimport the reference file.
Hello - if I follow, you are trying to detach the active model…?
-Pascal
I try to make a video asap.
PS: Yes, I was trying to detach and attach but a warning “Work Session Attach Failed” pops up
Hello - ok - well, there the active model is not an attached model, so it cannot be detached. I’m not clear on what it is you are trying to accomplish.
-Pascal
I was trying to be confident and looking at what the worksession was capable of.
Let say
I try to re-attach the file.
Video
Bug report: RH-57515
