Note that every time you see a vwAddTag error, the message should be different if it was supposedly fixed already. The reason is that for every kind of parser that gets added to XenForo, VaultWiki needs to add a class to extend that new parser too or a security vulnerability might open. Because of this, we decided early on during beta that it would be better to get a fatal error in these cases than to let users possibly make vulnerable posts. The idea was that we would start suppressing these errors for the gold release.
Once suppression is available, VaultWiki should be able to detect if the un-extended class might have a security vulnerability when used in conjunction with VaultWiki and instead just disable itself in those cases. This mechanism was supposed to be included as of RC 1 but apparently it wasn't working properly. I suspect it had to do with creating multiple instances of the BB-Code parser with different rules during save actions (on save: parse for quotes, @mentions, etc. then parse for email notifications). For these cases, I believe the error suppression is finally fixed in RC 4.
I've just enabled RC 4 for download, so you can see if it resolves the issue.