WOW, what timing! I just read the following article this evening in October's PC Magazine.
In both Outlook and Internet Explorer, right-clicking and choosing View Source currently does not work on my computer. The source for the message or page is not displayed, though the feature worked until recently.
There are many possible causes for this.
If your browser cache is full, View Source can fail. To see if this is the case, select Internet Options from IE's Tools menu, click on the General tab, and click on the Delete files button in the Temporary Internet Files pane.
View Source is always disabled when a page has not finished loading (a clue here would be that File ¦ Save As is also disabled). Again this is probably not the cause.
If Notepad.exe is missing from the Windows folder, View Source will fail.
View Source can fail if the TEMP or TMP environment variable points to a nonexistent folder. Open a command prompt and enter the commands SET TEMP and SET TMP to view the values of these variables.
A Registry setting can restrict the availability of this command. Launch REGEDIT from the Start menu's Run dialog and navigate to HKEY_CURRENT_USER\Software\ Policies\Microsoft\Internet Explorer\ Restrictions. Look in the right-hand pane for a value named NoViewSource. If present with data set to 1, double-click on it and change the data to 0.
A Registry setting may point to the wrong program to invoke for View Source. Launch REGEDIT and navigate to HKEY_LOCAL_MACHINE\Software\ Microsoft\Internet Explorer\View Source Editor\Editor Name. If this key exists, the data for the default value in the right-hand pane should be the full pathname of notepad, typically C:\windows\notepad.exe. If not, verify the correct location of notepad, double-click on the default value, and correct the data.
A Group Policy setting can disable the View Source menu item. From the Start menu's Run dialog, launch GPEDIT.MSC. If this command is unrecognized, a Group Policy setting is not the cause. Otherwise, in the Group Policy Editor, navigate to User Configuration\Administrative Templates\ Windows Components\Internet Explorer \Browser menus. In the right-hand pane find the item View menu: Disable Source menu. If it's set to Enabled, change it to Disabled.
Note that the Temporary Internet Files problem (the first item) is the most common reason for View Source to fail. If that doesn't help, go through these possibilities until the problem is cleared up.
Hope one of these solutions fixes the problem for you.