Vista can't access password protected network share

LAN network created by DSL-Router AVM FritzBox 7270.
One LAN client - windows xp pro sp3
One WLAN client - vista business 32bits sp1

USB mass storage connected to router. Router shares the drive
using samba server. Win xp has no problems while accessing this drive.
Vista can access the drive only if it is not protected by password.

I asked the manufacturer for NTLM issue.
It was the customer support.
They claim my router supports NTLM as well as NTLMv2.
They claim also the reason is some where in my vista networking
settings. Not the router itself.

There are no official procedure for updating the router's SMB server.
One can update the whole firmware only.
I avoid patching the router soft as long as the guarantee doesn't expire.


Which network settings should I check ?