I did some further investigation and it looks like net use does no longer work with Windows 2003 Server, if I like to map a share on a 2008 or 2012 server it works fine. Anyone got an idea, why this no longer works?
You have to change LMCompatibilityLevel to Connect Win8.x SE to Server 2003 or below.
[HKEY_LOCAL_MACHINE\Tmp_SYSTEM\ControlSet001\Control\Lsa]
"LmCompatibilityLevel"=dword:00000002
Value: LMCompatibilityLevel
Value Type: REG_DWORD
Valid Range: 0-5
Description: This parameter specifies the type of authentication to be used.
Level 0 - Send LM response and NTLM response; never use NTLMv2 session security
Level 1 - Use NTLMv2 session security if negotiated
Level 2 - Send NTLM authentication only
Level 3 - Send NTLMv2 authentication only
Level 4 - DC refuses LM authentication
Level 5 - DC refuses LM and NTLM authentication (accepts only NTLMv2)
By default the value is set to 3, to connect to Server 2003 and below change to 2.