i dont know you found the solution or not but for me following is working :-
rest same as yours , try this simple if still it didn't worked for you.
hope it helps.
wildcards are a dangerous thing if not used properly.
please exlpain, I'm pretty new at this.
you have overlapping rules because you used a wildcard.
i havent tested this but my first guess would be you need to sperate those rules a little more and have only one rule applied to the admin folder. rewrite the rules so the wildcard rule doesnt preceed the admin rule... if that doesnt work move the admin folder out of the folder you are using the wildcard in or rewrite the rules to not include the admin folder in the wildcard rule.
that is just where i would start.