I am not Allan but I will answer anyway.
I am not familiar with Yahoo mail but did you only update your
computer two days ago? If so, see if you think this is relevant:
Problems in Windows Explorer or the Windows shell after you install
security update MS06-015 (15 Apr-06)
http://support.microsoft.com/default.aspx/kb/918165
Microsoft Security Bulletin MS06-015
Vulnerability in Windows Explorer Could Allow Remote Code Execution
(908531)
http://www.microsoft.com/technet/security/bulletin/ms06-015.mspx has
been revised to v1.2 to reflect the issues in KB918165.
From the FAQ section:
"On Tuesday, April 25, Microsoft will issue a targeted re-release of
the MS06-015 update."
Now may not be the time to learn Regedit.
I suggest you use a .reg file already done for the purpose.
http://patch-info.de/WinXP/Downloads/KB908531_Share-To-Web.zip
Unzip it, extract the .reg file to a folder, right-click it and select
Merge and confirm when asked.
....Alan