Here's another odd App-V error you could possibly run into. The first time I read this I wondered how this could ever possibly happen but I guess it happened to someone otherwise it wouldn't have been reported to us:
Issue: If an App-V application package OSD file’s CODEBASE GUID reference is changed to a GUID from another package you may receive the following error message when you attempt to launch the application:
Application Virtualization Error
The Application Virtualization Client could not launch Application
The operation failed because of a package mismatch. If the problem persists, report the following error code to your System Adminstrator.
Error code: 4505CD-14906F0A-00000121
Example: Open up the App-V client OSD file cache for Application A and copy the OSD CODBASE GUID from application A and paste it to the CODEBASE GUID of application B and then try to launch application B. You should receive xxxxxx-xxxxxx44-00000028 error reference in the following KB article but instead you receive the less informative message above.
931101 - Error message when you try to start an application in Microsoft SoftGrid: "Error code: xxxxxx-xxxxxx44-00000028" http://support.microsoft.com/default.aspx?scid=kb;EN-US;931101
Cause: This is an unsuspected error due to mismatching CODEBASE GUIDs between the OSD and the package. Verify that the OSD Codebase GUID=XXXX…. Statement represents the correct GUID for the package. This will happen if you copy the OSD CODBASE tag GUID from the OSD file of application A to the OSD file of application B and then try to launch application B.
Resolution: Copy the GUID attribute of the CODEBASE element from a working .osd file of the same sequence. Then, paste the attribute to the problem .osd file. Next open the sequence with the Sequencer and un the Shortcut Wizard to create a new OSD file.
J.C. Hornbeck | Manageability Knowledge Engineer
Here's another odd App-V error you could possibly run into.  The first time I read this I wondered
Funny, I just faced this on 5 packages, where softpkg guid is different everytime but codebase guid is same.... these packages were build from scratch on freshly build sequencers and no one ever modified osd files manually. My bet is on softgrid bug, but quite annoying one :] Slight issue is that as per statement above I should copy codebase guid from working .osd file of the same sequence which of course we dont have since this was one time sequenced app. So unless there is a way how to generate this number manually we are back with rebuild the app and hope for the best
This happened to us using on windows 2008 r2
App-v 4.6 sp1