FTP server 550 error

We are running Win FTP on our ftp server but are having a peculiar issue.  Its "home" directory goes to a mapped drive on our LAN.  I've set up a user with the appropriate permissions to the "home" directory and it works fine for a few days but then whenever someone tries to log in and upload a file it won't allow them to.  The log files always show that the user logs in fine but gets a "550 can't access file" error.  The only way to fix this is to shut down the ftp server program then re-launch it or reinstall the app.  I thought maybe another ftp program would solve the issue but it doesn't.  I'm sure it's a permissions problem but I've set them to wide open everywhere I could to try and track down the problem without any success.  I have also disabled my antivirus firewall as well.  Also, the ftp app we're using (Win FTP) in this configuration ran flawlessly for over a year but recently just started having this issue.
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Hugh FraserConnect With a Mentor ConsultantCommented:
The 550 error may indicate that the network share's no longer mapped (it's generally file not found).
As a test to ensure that network connectivity stays up, try logging in with the same account the ftp server's running as and opening Microsoft Explorer to the directory being served by the FTP server. Leave it logged on and open until you get the FTP error, and check to see if Explorer can still see the share.

If not, there's a timeout (perhaps an inactivity timeout) disconnecting the FTP server from the share. There will probably be a message in the system event log.
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