Windows Live Mail storage files missing or locked

I have been using Windows Live Mail for over a year and have carefully stored messages in numerous folders. Suddenly several of these folders disappeared. When this happened once before, I was able to locate the storage folders and import the messages. This time, some messages--from Nov. 13, 07, through Aug. 19, 08--are missing. When I do a "search," the messages show up. I then navigate to the specified locations but get error 0x800CCF65.3, "The file (name) could not be opened because it does not exist or is being used by another program."

Microsoft notes this problem in its knowledge base but says it is caused by a GFI Mail Security antivirus program for Microsoft Exchange etc. Since I do not use either of these programs, their workaround will not work. I could find no helpful references through the Microsoft communities, Google, Yahoo or elsewhere. I think the messages still exist but are locked somehow. Do you have any idea what is happening or whether it can be fixed?

Thank you.