Installing Exchange 2007 SP2 on SBS 2008

You run into issues installing Exchange 2007 SP2 on SBS 2008 until you add the following key and DWORD to the registry.

To create the E12SP2READY registry value, follow these steps:

1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINESoftwareMicrosoftSmallBusinessServerExchange

   Note If the Exchange subkey does not exist, you must create it. To do this, follow these steps:

   1. Right-click SmallBusinessServer, point to New on the Edit menu, and then click Key.
   2. Type Exchange and then press ENTER.
3. After you select the Exchange subkey that is specified in step 2, point to New on the Edit menu, and then click DWORD Value.
4. Type E12SP2READY, and then press ENTER.
5. Right-click E12SP2READY, and then click Modify.
6. In the Value data box, type 1, and then click OK.
7. On the File menu, click Exit to exit Registry Editor.

Full article at Microsoft – http://support.microsoft.com/kb/973862