Win2003 share being lost/dropped intermittently on Win7

Several Win 7 64 bit workstations are randomly losing connection to one of our shared drives from a Windows 2003 server. 1) In Windows Explorer for example trying to access \caedc1\Macshare results in:

Windows cannot access \\caedc1\Macshare
Error code: 0x80004005
Unspecified error

2) Then net use results in the following seemingly, the share is still there:

Status       Local     Remote                    Network

-------------------------------------------------------------------------------
OK           H:        \\caedc1\users$\me        Microsoft Windows Network
OK           S:        \\caedc1\shared$          Microsoft Windows Network
OK           Z:        \\caedc2\T-L-Video        Microsoft Windows Network
OK                     \\10.0.225.240\Macshare   Microsoft Windows Network
OK                     \\caedc1\users$           Microsoft Windows Network
The command completed successfully.

3) Pinging the DNC path works:

C:\Users\me.CAE>ping caedc1

Pinging caedc1.xyz.com [10.0.225.240] with 32 bytes of data:
Reply from 10.0.225.240: bytes=32 time=17ms TTL=128
Reply from 10.0.225.240: bytes=32 time<1ms TTL=128
Reply from 10.0.225.240: bytes=32 time<1ms TTL=128

Ping statistics for 10.0.225.240:
    Packets: Sent = 3, Received = 3, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 0ms, Maximum = 17ms, Average = 5ms

4) I can also access the files if I use the IP address like this, in Windows Explorer: \\10.0.225.240\Macshare\

5) Trying to map another temporary share via the net use command results in this:

C:\Users\me.CAE>net use t: \\caedc1\shared$
System error 64 has occurred.

6) Per this thread, IPv6 is disabled & "Client for Microsoft Networks" still exists.

7) Windows Firewall is disabled.

8) We use Symantec Endpoint Protection as our AV.

9) A reboot always fixes the share.