I've seen questions posed in the past about Vista locking files - and I am having the exact same problem, which I posted about a while ago.  Today it happened to me again.

There appears to be no pattern as to why this happens.  Was happening to me continually until a few weeks ago. Then it stopped without me taking any course of action (just putting up with the annoying bug is all I could do).

You just have to remember to save the file under a different name to ensure that you don't lose your original file.  The original file does not appear in the File Manager window (after you close down DW, nor does it appear in the Trash bin - it's just gone).

Initially I thought it may be due to having the file open, checking it in Firefox and possibly FF taking over the file, so it gets locked by DW.  Today, I only opened the file (no checking in a browser at all) made a minor correction and I was locked out of the file.

Co-incidentally, a few hours ago, I found a website via twitter where this seems to be a known issue, but no there appears to be no response from Adobe about this bug.   http://www.sherylcanter.com/wordpress/2009/05/locked-vanishing-files-i n-dreamweaver-and-indesign/

Previously, I used to restart the pc and I'd lose the file altogether (as explained above).  After reading the above website, I'm going to leave DW open for a while to see if it's true about the file 'unlocking itself'.  Thankfully,, this time, I did backup the file just in case.  In the past I'd lost a fair amount of work, that I'd had to recreate - very annoying !!

I thought I'd post up a graphic of the error messages - to see if others are seeing the same thing. This will need to be bought to the attention of the DW tech team, but not sure how they can address the issue as it is a difficult thing to reproduce on a consistent basis.

AN UPDATE;  Checked for the file in Windows File manager - the index.html page is not listed in the sitefolder.  Back to Dreamweaver, you can still see the locked file, do a refresh and the index.html file has disappeared.

I open index2.html (the resaved version of index,html), rename it to index.html and it allows me to do so this time round.

PS:  At the same time I opened inner.html, made a change, no problems with the file locking.

Weird !!

Further update:

Just found a reply by David Powers here:  http://forums.adobe.com/thread/437034?tstart=30

I had tried to do a search using similar keywords when this started happening to me months ago - couldn't find anything at the time.

I even posted to a private forum where people should have known about this issue - but it was never responded to.

Will see if this fix works for me....  though I can't understand why it only does this occasionally - if someone needs to take control of the folder, surely it should be happening all the time.