Hi Duane,
If you are currently using hashed passwords or clear text passwords then changing the machine key will not cause any problems other than it will force you logged out so you would have to login again.
If you are using encrypted passwords then when you change the machine key it will no longer be able to decrypt and that would cause errors and prevent you from logging in.
So if you are currently using encrypted and you want to change the machine key you must do the following:
1. backup the db in case anything goes wrong, clear the mojoportal log so that you can tell new errors from old ones.
2. stay logged in and change the password format to clear text (this process may take a few minute if you have lots of users).
3. Open a different browser ie if you are using IE on the first browser use Firefox or Chrome and make sure you can still login using a different browser after changing to clear text. Stay logged in on the original browser just in case.
4. If you can still login after changing password format, then backup your machine key and replace it with a new one. This may actually force you to be logged out when you do this, but you should be able to login again.
5. Now once you have changed the machine key and have logged in again, you can change back to encrypted password format.
If something goes wrong download your log from /Data/currenntlog.config as it may have clues what went wrong, then you could send me the log if needed. Hopefully nothing will go wrong.
Hope that helps,
Joe