I've been working with the same file now for a couple of months, now all the sudden I can't it to open.  I get an error message that says - "file failed to open" - any advice?

Sesame only allows one server to access any one .db/.dat file at a time. To insure that more than one server cannot access that same file, we have a flag in the file indicating that a server does or doesn't have it open.

Sesame never leaves a file actually open, even while you are using it, unless it is being actively read or written. It does this to avoid the corruption which is inevitable if a file is in an "open" state when the power goes off or the network goes down - especially in Windows where the caching of file contents is unstable. So, we reopen the file for each use, and close it again when finished (usually less than a tenth of a second later).

If an application file is not "closed" inside Sesame, whether by opening a different application, shutting down the server, using the "close" pulldown choice, or exiting standalone Sesame - that "in use" flag is left "set". If no one else is using the application file at the time, there is no harm in "unlocking" a locked Sesame application.