System error 58 while accessing shares on Windows 7 from XP

When Windows XP tries to access a share on a Windows 7 computer and returns «System error 58», the cause is a mismatch in the NTLM authentication level. The setting must be aligned on both sides: set the following on both the XP and the Windows 7 machine, then restart.

1. Run gpedit.msc (or secpol.msc to open the security policy editor directly).
2. Expand Windows Settings → Security Settings → Local Policies → Security Options.
3. Locate Network Security: LAN Manager authentication level in the list and double-click it.
4. Change the setting from «Send NTLMv2 response only» to «Send LM & NTLM – use NTLMv2 session security if negotiated».

After the restart the share opens normally from XP.