Disable / Enable NTLMv2 in Windows 7/Vista clients:
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- Click Start > All Programs > Accessories > Run and type secpol.msc in the Open box, and then click OK.
- Click Local Policies > Security Options > Network Security: LAN Manager authentication level.
- Click Send LM & NTLM - use NTLMv2 session security if negotiated.
- Click Apply.

Changes should be active immediately, without a reboot.