Missing Xref

I am having a very strange problem with an xref i have not come across before, I have a two storey building with 3 xrefs on ground floor drawing, two of the xrefs are working fine but 1 of them is missing when i open the drawing and i need to re-attach it not unloaded or not found just completly gone, it does not happen all the time but i would like to find out why it is happening at all.

Autocad 2008

Possible pathing problem? Are the drawings stored on a network?

yes xrefs are on the network in folder 'xrefs' its strange that only one of the xrefs is doing this.... its like the xref has just been dettached but i know that has not happened.

And you come by this knowledge how? Do other people access the same drawing?

because my work colleague is not here this week so its only myself, like i said it doesn't happen all the time, the drawing was fine last night but when i opened it this morning the xref was missing....

What is VISRETAIN set to?

What error message do you get on the command line (if any)?

Have you tried using the REDIR command to update the paths of your xrefs?

Does your version of AutoCAD have an XREF Path option and/or an External References palette?

Yes it has xref path option, VISRETAIN is set to 1 in xref and 0 in host drawing, would that be the problem??

No, I don't believe so. Just checking.

You didn't happen to place the Xref on a layer in the drawing that is turned off by any chance?

What is Path type set to? Full path or Relative path?

By the way, what is the Saved Path look like for this particular drawing? Could you type it out for us to see?

definatly not a layer turned of, if it was the xref would still show up on the xref dialogue box.

its full path, my understanding is relative path searches for the xref oncde the drawing structure is the same if the host drawing is moved.

the xref has not been moved or had its name changed

maybe the drive the file was on got changed, just a thought.