Validation will "lock" the files against deletion. There's also an additional level of locking, because rulesets are required by the target catalogues, so you must also (first!) in-validate the target catalogue.

If you receive the following warnings:
  • The file <filename> is protected by validated catalogue(s) '<cat_filename>' which must first be unvalidated.
  • The file <filename> must first be unvalidated.
You should:
1) in-validate the target catalogue
2) in-validate the ruleset
3) finally delete the ruleset