Error with ACAccount and TWRequest

This is my code

TWRequest *twRequest = [[TWRequest alloc] initWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@%@", kTwitterURLBase, kTwitterMethodHelpConfiguration]]
                                           parameters:nil
                                        requestMethod:TWRequestMethodGET];

[twRequest setAccount:[self twitterAccount]];

[twRequest performRequestWithHandler:^(NSData *responseData, NSHTTPURLResponse *urlResponse, NSError *error) {

     // Handling

}];

The method twitterAccount

- (ACAccount *)twitterAccount {

    NSString *identifier = [[Session getInstance] selectedAccountIdentifier];
    ACAccount *account = nil;

    if ([identifier length] > 0) {

        ACAccountStore *accountStore = [[ACAccountStore alloc] init];
        account = [accountStore accountWithIdentifier:identifier];
    }

    return account;
}

As debugger says, the account is correctly returned but when I print it in the console I get nothing, a blank space; but the account object has a reference.

Just after the request begins to be performed I get an EXC_BAD_ACCESS error. The stack says that the error occurs when sending a wrong message [ACAccount accountType].

It's obvious that is a memory problem, and I new with ARC so I guess that the problem would be there.

Any help?

I don't know why the hell I have to do this but if I declare an instance variable for the ACAccountStore to be retained and change the method this way

- (ACAccount *)twitterAccount {

    NSString *identifier = [[Session getInstance] selectedAccountIdentifier];
    ACAccount *account = nil;

    if ([identifier length] > 0) {

        if (accountStore_ == nil) {

            accountStore_ = [[ACAccountStore alloc] init];
        }

        account = [accountStore_ accountWithIdentifier:identifier];
    }

    return account;
}

all goes perfect. Why? :\