Inexplicable “abort: untracked files in working directory”

[Pietro Moras]

I'm getting a, to
me, unjustified and therefore inexplicable:
“abort:
untracked files in working directory differ from files in requested
revision”
when
navigating along the development history of a versioned project. 
That
is:  going back and forth between different Changesets with such a: 
“update -v -r <Id>”
command. 
All that without introducing any whatsoever change into the
Project.
How to interpret
such an “abort” and, more important, how to prevent it?



Of course the
Project comprises more than one file, all tracked and committed ok.
Plus, by try-and-error, I “discovered” that just deleting the
named file (well existing into the Working Directory) I could execute
the same “update -v -r <Id>” command ok, with a
consequent re-creation of the lamented file. 

Anyhow, a
behavior easily reproducible and about which I could easily offer
further details, if asked.
It's serious, as
I'm losing confidence in the whole Mercurial system. Thanks. 

 - P.M. 		 	   		  
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