I am working with a model that has several (11) 'levels'. for some reason I am no longer able to adjust the order of these levels using the up/down arrows in the 'Modify Level' dialog. A few days ago I was able to move a level from top to bottom but now all levels seem to be stuck.

I can still adjust the order of levels in my old files and also with a new file but this particular file seems locked. File size is ~20MB.

Note that all my levels are at the same elevation, height and floor thickness. I am therefore using levels as 'layers' rather than traditional levels.

Any ideas?

My next step is to start again with a new file and copy each layer into that but I'm interested to know what has gone wrong with this file.