I found my answer here:
http://social.answers.microsoft.com/Forums/en-US/w7files/thread/cc378149-8765-498a-9480-b1b494e1a1a9
In effect:
This issue can be caused if an invalid registry key for the Start Menu grouping values gets written to the following registry key:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FolderTypes{ef87b4cb-f2ce-4785-8658-4ca6c63e38c6}\TopViews{00000000-0000-0000-0000-000000000000}
The incorrect registry value is the GroupBy value, the incorrect value is most often “System.Null” but can appear as other values. The correct value should be “System.StartMenu.Group”
You can resolve the issue by follow one of the methods below:
Method 1: Delete the entire key:
To browse to and delete the registry key follow the steps below:
1. Click Start
2. In the Search programs and files box, type regedit
3. In the Programs list, click regedit.exe
If you are prompted for an administrator password or confirmation, type the password or click Continue.
4. Browse to and click to select the following registry subkey:
5. HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FolderTypes{ef87b4cb-f2ce-4785-8658-4ca6c63e38c6}
6. In the left side of the window right-click GroupByand click Modify
7. Change the value to System.StartMenu.Group and click OK, then close the registry editor
You'll need to reboot your computer for this change to take effect.
Method 2: Add the correct value of GroupBy value:
Follow the steps below to add the correct value to the GroupBy value:
1. Click Start
2. In the Search programs and files box, type regedit
3. In the Programs list, click regedit.exe
If you are prompted for an administrator password or confirmation, type the password or click Continue.
4. Browse to and click to select the following registry subkey:
5. HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FolderTypes{ef87b4cb-f2ce-4785-8658-4ca6c63e38c6}\TopViews{00000000-0000-0000-0000-000000000000}
6. In the left side of the window right-click GroupByand click Modify
7. Change the value to System.StartMenu.Group and click OK, then close the registry editor
You'll need to reboot your computer for this change to take effect.
Ken Smith