[XP] "You reach the registry size limit (RSL)" message
In Microsoft Windows Server 2003 and in Microsoft Windows XP, the Registry Size Limit (RSL) functionality has been removed. There are no longer any limits on the total amount of space that may be consumed by registry data (hives) in paged pool memory, and in disk space.
http://support.microsoft.com/?kbid=292726
However is possible to receive at logon, the message "The Registry Size Limit has been reached". This could happens because an application, like antivirus program, or a driver don't correctly unload from the memory. To fix this behaviour you need to run the tool User Profile Hive Cleanup Service (UPHClean)
http://support.microsoft.com/kb/837115/en-us
Italian version