I get a dozen of these reports when I scan the registry with CCleaner. I've checked, and the dll files really don't exist in the locations reported by the registry keys.
Is it okay to modify these registry keys, so that they would point to where the dll files are located (though its kind of confusing since there are two (or more) versions of these dll files, usually one coming from .net Framework 2.0 and the other from .net Framework 4.0)?
Anyone has some sort of experience after modifying these keys (I don't want to delete them, even though CCleaner reports that they should to be removed.)?

If it ain't broke.....

Well, they show as missing in CCleaner, and I've checked the files, the aren't there. I don't have any problems the way it is right now, however. :)
Just wanted to know if anyone has experience regarding modifying these registry keys.

I use CCleaner as well and delete the problem entries on XP, Vista and Win 7. They usually show up after windows update, Adobe updates and Java updates. You can create a backup .reg file prior to deleting the entries. I believe it asks just prior to deletion and you can skip the backup if you want. If you have problems just double click the .reg file to put the entries back into the registry.
Spybot Search & Destroy has a similar feature but doesn't allow for a backup.
Edit: I should mention that I have used CCleanup since the first release and have never had a problem due to deletion of the problems it finds.