Windows 7: Shared Folders dropping after file transfers

Problem: Shares from Windows 7 machine dropping out if files are transferred from a client machine to the shared folders. They become inaccessible afterwards(all shares, not just the one accepting the transfer).

Setup:



"SMB server" - Windows 7 (shares are located on an external 2TB WD MyBook Mirror Edition set up in a RAID 1 config)

Client 1: Windows 7
Client 2: XP
Client 3: OS X Tiger
Client 4: OS X Snow Leopard
Client 5: OS X Tiger

Problem occurs regardless of which client is used. Initially, I thought it was an error due to power management as it seemed to only occur after several hours of inactivity, however I had changed everything I could find that could have affected it. But, I have seen it happen now twice today after transferring files. Thanks for any ideas.