psexec giving access denied

[popey]

hello,

i am using psexec and i am getting access denied.....both the system are win xp pro.....both the accounts are administrative ......i have made some changes in registry.......

1) for Server ADMIN$ Share

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanManServer\Parameters

Name: AutoShareServer

Data Type: REG_DWORD

Value: 1

2)For the Remote Registry service

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RemoteRegistry

Name: Start

Value: 2

the syntax i used is .....psexec -u username -p password \\targetpc cmd.exe

username and password are the one used on target pc to login ........the guest account is also on .......i tried it by creating same account with same username and psswd but it didnt work......plz tell what is the reason..........

[infof]

Psexec very often does't work on the Win XP SP2( If computer is not member Domain) .