Smb file sharing

We have in our company data center two Macs, a Power PC 8GB ram with Leopard 10.5.8 and a Mac Pro Quad Core Nehalem 32GB with Mountain Lion 10.8.3 and OSX Server 2.2.1.

The Power Pc SMB File Sharing, with the limit of 10 concurrent users, it works perfectly.

Instead, the Mac Pro SMB File Sharing drops randomly SMB sharing with the consequent loss of the changes made by Client to opened files.

Is there anyone else with the same problem?

Is there any solution, in addition to turn off the Mac Pro and switch to a Windows server?