The IgnoredApps key is used to mark an inconsistency between a locally-cached .OSD file which is either corrupt or not accessible for various reasons and its original location. There could be many reasons for this, including but not limited to:
Malformed XML, File corruption, Access Permissions erroneously placed on the cache
The Key is located in the registry here: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Softgrid\4.5\Client\IgnoredApps — You’ll need to remove the entry(s) under this key manually. Once you corrected the underlying issues, remove the entries under the keys. You will need to restart the Application Virtualization Client service upon doing so.
More info: App-V blog