Click Start, click Run, type regedit, and then click OK.
Locate and then click the following subkey:
[div class="note" class2="typo-icon"]HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters[/div]
In the right pane, locate the AllowSingleLabelDnsDomain entry. If theAllowSingleLabelDnsDomain entry does not exist, follow these steps:
On the Edit menu, point to New, and then click DWORD Value.
Type AllowSingleLabelDnsDomain as the entry name, and then press ENTER.
Double-click the AllowSingleLabelDnsDomain entry.
In the Value data box, type 1, and then click OK
Quit Registry Editor.
You should be able to join the machine to the domain.