Client machines may fail to boot into PXE in SCCM SP2

http://support.microsoft.com/kb/2019640

1. Click Start, type regedit in the Start Search box, and then click regedit in the Programs list.
   Note If you are prompted for an administrator password or for confirmation, type the password or provide confirmation.

2. Locate and then select the following registry subkey:
   HKEY_LOCAL_MACHINE\Software\Microsoft\SMS\PXE

3. Right-click CacheExpire, and then click Modify.

4. Configure the cache expire value. For example, set the value to 120 seconds (two minutes). To do this, follow these steps:

   1. In the Value data box, type 120.
   2. In the Base area, click decimal.
   3. Click OK.
5. Exit Registry Editor.

6. Restart the Windows Deployment Services Server service.