Error 211 - file no longer available

[striker]

I am using VIM 7.0 on Windows XP with network access.  I edit a  
file   e: h:/notes/todo.otl.
If VIM is inactive for a few minutes (less than 5) I receive a  
message E211: File "todo.otl" no longer available.
I am still able to write the file to the network though so the file  
is still available.

To correct a previous E297 error, I changed the location of the swap  
file to my local HD.  :set dir=c:\\Temp

I have been unable to find a fix or a reason why the E211 error comes  
up.   Any suggestion on what to check?

TIA,
Kevin