ERROR message: No response received from workstation???

Hello support team,

While the SDP is scanning the workstations, almost all workstations have this error message:
'' No response received from workstation. Probably the workstation might be
switched off or does not exist. ''
I searched the related topics including this error message in the forum page but there is no solution except the general solution. And I would like to indicate that;
The workstations are XP machines
The workstations do not have firewall enabled
The workstations do not have firewall service enabled
I can go \\machinename\c$ from the machine to the SD+ server.

What should we do to get rid of the error message and finish scanning successfully? Do you want me to send the log file???

Regards.