The specified domain either does not exist or could not be contacted

Hi!

3 sites
1)
2 Windows 2003 Servers (two DCs)
Windows 2003 Server + SQL Server 2000
2)
Windows 2003 Server (DC)

3)
Windows 2003 Server (DC)

Total about 250 windows XP workstations


Since about two weeks from time to time we encounter a problem in our domain. Once or twice a day (not every day but now becoming more frequent), usually in the morning I receive a call from various persons complaining that they can't login. I connect through VNC and see that they all get the same error: "The specified domain either does not exist or could not be contacted" (I have an italian version of windows so am not sure if the translation is correct 100% as in english version). The only way to get the machine back to work is to log in as local Administrator, connect it to a workgroup, then join back to domain.

There's a fact that I've found in system log of the latest machine I had this problem with:

English translation from eventid.net:
Event ID: 5801
Source Netlogon  
Type Error  
Description Attempt to update DnsHostName and HOST Service Principal Name (SPN) attributes of the computer object in Active Directory failed because this computer account name <name> could not be mapped to the computer object on Domain Controller <server>. Not having SPNs registered may result in authentication failures for this computer. Contact your domain administrator. The following technical information may be useful for the resolution of this failure:
DsCrackNames status = 0x0 crack error = 0x2.  


Someone has already encountered this issue?

Thanks in advance!