A false positive of AVG Anti-Virus crashed Windows XP "again". The antivirus flagged a Windows system file wintrust.dll as Generic32.FJU Trojan horse. When user opts to clean the infection or remove the file, Windows XP fails to boot.
AVG has released new virus definition and fix the error but those who have already removed the file are recommended to boot their PC with Windows XP CD in order to copy the original wintrust.dll file back to the system32 folder.
Source: AVG forum