"The RegClean utility is no longer supported by Microsoft and has been removed from all Microsoft download sites. This was done for legitimate compatibility reasons with certain applications and Operating Systems. The RegClean utility was originally supplied with Microsoft Visual Basic version 4.0 for Windows. The last version of RegClean was 4.1a (build 7364.1) released on March 13, 1998 (RegClean.exe is dated December 30, 1997). During this time the latest Operating Systems were Windows 95 OSR2.1 and Windows NT 4.0. Windows 98 was not released until June 25, 1998. Compatibility with any Operating System besides Windows 95 and NT 4.0 was never substantiated, especially Windows XP. It is very dangerous to run a Registry Cleaner that was never certified to run on your Operating System since removing the wrong Registry Keys can break Applications and the Operating System. RegClean breaks functionality in the following Applications:
- Microsoft Access 2002 Standard Edition
- Microsoft Excel 2000 Standard Edition
- Microsoft FrontPage 2000 Standard Edition
- Microsoft Office 2000 Developer Edition
- Microsoft Office 2000 Premium Edition
- Microsoft Office 2000 Professional Edition
- Microsoft Office 2000 Small Business Edition
- Microsoft Office 2000 Standard Edition
- Microsoft Office Access 2003
- Microsoft Office Access 2007
- Microsoft Office Basic 2007
- Microsoft Office Basic Edition 2003
- Microsoft Office Enterprise 2007
- Microsoft Office Excel 2003
- Microsoft Office Excel 2007
- Microsoft Office FrontPage 2003
- Microsoft Office Home and Student 2007
- Microsoft Office InfoPath 2007
- Microsoft Office OneNote 2007
- Microsoft Office Outlook 2003
- Microsoft Office Outlook 2007
- Microsoft Office PowerPoint 2003
- Microsoft Office PowerPoint 2007
- Microsoft Office Professional 2007
- Microsoft Office Professional Edition 2003
- Microsoft Office Professional Plus 2007
- Microsoft Office Project Professional 2007
- Microsoft Office Project Standard 2007
- Microsoft Office Publisher 2003
- Microsoft Office Publisher 2007
- Microsoft Office SharePoint Designer 2007
- Microsoft Office Small Business Edition 2003
- Microsoft Office Standard 2007
- Microsoft Office Standard Edition 2003
- Microsoft Office Student and Teacher Edition 2003
- Microsoft Office Ultimate 2007
- Microsoft Office Visio Professional 2007
- Microsoft Office Visio Standard 2007
- Microsoft Office Word 2003
- Microsoft Office Word 2007
- Microsoft Office XP (Setup)
- Microsoft Outlook 2000 Standard Edition
- Microsoft PowerPoint 2000 Standard Edition
- Microsoft Visual InterDev 6.0 Standard Edition - Microsoft Word 2000 Standard Edition
- Microsoft Windows Media Player
This issue occurs for any Microsoft Windows Installer product on which the program's installation state is set to Installed on First Use."
Source - XP Myths