Sharepoint 2010 Error Group cannot be found

Hi all,

I have a customer who has decided to use SharePoint 2010 on they're sbs2008 server. Was working fine until last week. No idea was has happened but when you now try and open the Central admin console you receive an error Group Cannot Be found.

Have checked the groups and they seem fine and also checked the IIS permissions and they are fine.

I'm not a SharePoint GURU and any help would be much appreciated.

thanks David.