It is probably a secret entry that Cakewalk has entered in the registry. There is no certain type to look for.
Since RegVac cleans so much, you must narrow things down. You can go into the Scan and Clean section of the Advanced Zone and run one tool at a time (by checking only one item and then clicking on the Scan and Clean button) until you find the tool that messes up Cakewalk. Then go to the RegVac directory in Windows Explorer and rename the current undo file and run that tool again. Then compare the two undo files (the first one should have the bad entry in it, the second one will not). Hopefully, that will help you find the bad entry. If not, you can send the two undo files to me and I will take a look at them. Lately I have not been too successful in finding bad entries because RegVac removes so much that it is like trying to find a needle in a haystack.
If you do find out which one is the bad entry, please let me know so I can permanently keep RegVac from removing it.