I had the same problem and I think my solution will fix it.

****PROBLEM****
===============

First off, I have a dual boot of XP and Vista. I first installed XP on drive C: then installed Vista on drive D:. I then imaged my whole hard drive with Acronis True Image Home V11. When I restored the image and try to load Vista, I get the following problem in a dialog.

Title Bar: Rundll32.exe Entry Point Not Found
Dialog: The procedure entry point SdbGetAppCompatDataSize could not be
located in the dynamic link library apphelp.dll.

****SOLUTION****
================

- After re-imaging, Log into Vista, and avoid any dialogs that say restart the system.
- Open "regedit".
- Go to "KEY_LOCAL_MACHINE\SYSTEM\MountedDevices".
- Then rename "\DosDevices\D:" to "\DosDevices\CTemp:".
- Then rename "\DosDevices\C:" to "\DosDevices\D:".
- Then rename "\DosDevices\CTemp:" to "\DosDevices\C:".
- Restart system and log back into Vista, it should work now.
- I found the solution from the following website. ([url=http://www.vistax64.com/vista-installation-setup/131636-vista-64-dual-boot-changing-drive-letter.html]Vista 64 dual boot changing drive letter - Vista Forums[/url])

Basically, what's happening was when you originally had the dual boot system working, both the window systems renamed the primary drive. When you log into XP or Vista, they say their primary is C:, even though Vista's primary physical drive is in D:. Also, if you look into the drive C: when you're in XP or Vista, the system files are related to the loaded OS. However, when you re-image the hard drive with the dual boot, Vista will now say the primary drive is still C:, but if you actually look into C:, it has the XP OS system files, not the Vista's OS system files. So the solution above will correct this problem.