samba to Windows XP

problem:
net rpc commands do not work with my WinXp clients anymore.
They do still work with Win7 clients
The only change was an update to the samba server via apt-get dist-upgrade.

fix:
[global]
# This is the fix for the WinXp net rpc shutdown and backup failure
## Connection failed: NT_STATUS_ACCESS_DENIED
## smb_signing_good: BAD SIG: seq 1
# Default: client ipc signing = default
## When set to mandatory or default, SMB signing is required.
client ipc signing = disabled