A number of people who use Apple's "Mail" email client have installed the WideMail plugin to give an alternate message layout with the message list and message body being side-by-side, which is more appealing for wide-screen displays. After updating to 10.6.4, some of these people have found a couple of problems associated with Mail. The first is that the plugin no longer seems to work, and secondly the Mail subject line is blank in the message browser.
Fixing the blank subject line
While the message browser will show the usual "From", "Subject", "Date Received", and "Size" columns, the subject column shows no text for any listed messages.To clear this problem, you can take a more global approach or target a specific change that WideMail makes to the Mail application's settings. Either way, the following suggestions should clear up the issue:
Remove the "TableColums" attribute in Mail's preferences
Open the Terminal application and enter the following command, which should remove the "TableColumns" attribute that is causing the problem. This attribute was probably modified by WideMail to where the new version of Mail cannot properly read it when loading.
defaults delete com.apple.mail TableColumns
Remove Mail's preferences
If the previous command does not work, try removing Mail's preferences file and relaunching the program. This file is called "com.apple.mail.plist" and is located in the /username/Library/Preferences/ folder. Keep in mind that doing this will require you to enter your Mail account information again, but your downloaded messages and organized mailboxes should not be touched.
Get WideMail working again
In an Apple discussion thread, a user "gravesit" found a way to get WideMail working in the latest version of Mail. Apparently the incompatibility with the plugin is just a matter of the plugin's UUID not being in the list of supported ones in Mail.
Go to the /username/Library/Mail/Bundles/Contents/ folder.
Open "Info.plist" in a text editor and locate the "SupportedPluginCompatibilityUUIDs" key.
Add new string lines with the following UUID numbers:
E71BD599-351A-42C5-9B63-EA5C47F7CE8E (Item 6)
B842F7D0-4D81-4DDF-A672-129CA5B32D57 (Item 7)
Save and relaunch Mail.