“Access Denied” when joining a domain

While trying to join a machine which had previously been on a Windows Server 2003-hosted domain to a new domain hosted on Windows Server 2003 R2 (not sure if the change in OS is the cause of this issue), I kept getting “Access Denied”.

In C:\windows\debug\netsetup.log it says:

NetUseAdd to \\DC_FQDN\IPC$ returned 5
NetpJoinDomain: status of connecting to dc '\\DC_FQDN': 0x5
NetpDoDomainJoin: status: 0x5

The solution was to fire up regedit and change the value of HKLM\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters\enablesecuritysignature to 1, and restart.

Edit: Do this after leaving the original domain for a workgroup, because doing that resets it to 0.